Peter Aaen

Dr Peter Aaen


Reader in Microwave Semiconductor Device Modeling
+44 (0)1483 686123
30 ATI 02
PA: Jayne Nutbeen
+44 (0)1483 688706

Biography

Biography

Peter H. Aaen received the B.A.Sc. degree in Engineering Science and the M.A.Sc. degree in Electrical Engineering, both from the University of Toronto, Toronto, ON., Canada, and the Ph.D. degree in Electrical Engineering from Arizona State University, Tempe, AZ., USA, in 1995, 1997 and 2005, respectively. Prior to joining the University of Surrey, he was the manager of the RF Modeling and Measurement Technology team at Freescale Semiconductor Inc, Tempe, AZ, USA; a company which he joined in 1997 (then Motorola Inc. Semiconductor Product Sector).

He is a Senior Member of the IEEE, a member of the Microwave Theory and Techniques and Electron Device Societies, and is an active member of many technical committees including: IEEE Technical Committee (MTT-1) on Computer-Aided Design, technical program committee member (TPC) of the IEEE Conference on Electrical Performance of Electronic Packaging and Systems (EPEPS), and an executive committee member of the Automatic RF Techniques Group (ARFTG).

Research interests

His areas of expertise include calibration techniques for microwave measurements, development of package modeling techniques, development of passive and active compact models for the design of microwave power transistors and RFICs, and development of efficient electromagnetic simulation and optimization methodologies for complex packaged environments. His current work focuses on the development and validation of multi-physics based modeling methodologies for high-power and high-frequency electronic devices.

My publications

Publications

Sahu A, Devabhaktuni V, Lewandowski A, Wallis T, Aaen PH (2017) CAD-assisted microwave characterization of ink-jet printed CPW on PET substrates, Proceedings of 88th ARFTG Microwave Measurement Conference (ARFTG)
This paper describes the computer-aided-design (CAD)-assited microwave characterization of coplanar waveguide (CPW) lines formed by ink-jet printed technology on flexible polyethylene terephthalate (PET) substrates. A spacemapping technique is used to link the measured results with simulations and the mapping is used to extract the electrical properties of the ink and supporting dielectric spacer employed during measurements. Results indicate that the losses in lines are predominantly due to the loss tangent of the substrate and the conductivity of the ink. Estimates of the conductivity of the ink and the dielectric constant of the spacer used during measurement were obtained as 2:97 107 S/m, and 1.79 respectively.
Wood J, Lamey D, Guyonnet M, Chan D, Bridges D, Aaen PH, Monsauret N (2008) An extrinsic component parameter extraction method for high power RF LDMOS transistors, IEEE MTT-S International Microwave Symposium Digest pp. 607-610 IEEE
A new extrinsic network and extrinsic parameter extraction methodology is developed for high power RF LDMOS transistor modeling. This new method uses accurate manifold deembedding using electromagnetic simulation, and optimization of the extrinsic network parameter values over a broad frequency range. The new extrinsic network accommodates feedback effects which are observed in high power transistors. This improved methodology allows us to achieve a good agreement between measured and modeled S-parameters in the frequency range of 0.5 to 6 GHz for different bias conditions. Large-signal verification of this new model shows a very good match with measurements at 2.14 GHz. © 2008 IEEE.
Johnson EM, Aaen PH, Bridges D, Wood J (2012) The effects of material interfaces on thermal resistance values for high-power microwave transistors, 79th ARFTG Microwave Measurement Conference: Non-Linear Measurement Systems, ARFTG 2012 IEEE
In this paper, we examine the effects that the thermal interface between materials has on the thermal resistance extracted from electrical measurements. We also examine the consequent degradation in electrical performance. We present the characterization of the transistor under various thermal environments: mounted in packages, using various die attachments, and on-wafer. A wide range of thermal resistances are extracted and we demonstrate the importance of proper characterization during on-wafer thermal measurements. Finite-element simulations show that we can account for various thermal interfaces by changing the coefficient of thermal transfer from the semiconductor device to the material beneath it. Simulations are shown to be in good agreement with measured results. © 2012 IEEE.
Aaen PH, Wood J, Bridges D, Zhang L, Johnson E, Pla JA, Barbieri T, Snowden CM, Everett JP, Kearney MJ (2012) Multiphysics modeling of RF and microwave high-power transistors, IEEE Transactions on Microwave Theory and Techniques 60 (12) pp. 4013-4023
In this paper, we present a multiphysics approach for the simulation of high-power RF and microwave transistors, in which electromagnetic, thermal, and nonlinear transistor models are linked together within a harmonic-balance circuit simulator. This approach is used to analyze a laterally diffused metal-oxide-semiconductor (LDMOS) transistor that has a total gate width of 102 mm and operates at 2.14 GHz. The transistor die is placed in a metal-ceramic package, with bond-wire arrays connecting the die to the package leads. The effects of three different gate bond-pad layouts on the transistor efficiency are studied. Through plots of the spatial distributions of the drain efficiency and the time-domain currents and voltages across the die, we reveal for the first time unique interactions between the electromagnetic effects of the layout and the microwave behavior of the large-die LDMOS power field-effect transistor. © 1963-2012 IEEE.
Mkadem F, Ayed MB, Boumaiza S, Wood J, Aaen P (2010) Behavioral modeling and digital predistortion of Power Amplifiers with memory using Two Hidden Layers Artificial Neural Networks, IEEE MTT-S International Microwave Symposium Digest pp. 656-659
This paper presents a novel Two Hidden Layers Artificial Neural Networks (2HLANN) model for behavioral modeling and linearization of RF Power Amplifiers (PAs). Starting with a feedback loop principle model of a PA, an appropriate neural networks structure is deduced. This structure was then optimized to form a real valued and feed-forward 2HLANN based model capable of predicting the nonlinear behavior and the memory effects of wideband PAs. The validation of the proposed model in mimicking the behavior of a Device Under Test (DUT) is carried out in terms of its accuracy in predicting the output spectrum, dynamic AMI AM and AMIPM characteristics and the normalized mean square error. In addition, the 2HLANN model was used to linearize two 250 Watt peak-envelope-power Doherty PAs (DPAs) driven with 20 MHz bandwidth signals. The linearization of these DPAs using the 2HLANN enabled attaining an output power of up to 46.8 dBm and an average efficiency of up to 47.5% coupled with an Adjacent Channel Power Ratio higher than 50 dBc. When compared to a number of previously published behavioral and DPD schemes, the 2HLANN model demonstrated an excellent modeling accuracy and linearization capability. © 2010 IEEE.
Zhang L, Aaen PH, Wood J (2012) Portable space mapping for efficient statistical modeling of passive components, IEEE Transactions on Microwave Theory and Techniques 60 (3 PART 1) pp. 441-450
In this paper, a portable space-mapping technique is presented for efficient statistical modeling of passive components. The proposed technique utilizes the cost-effective model composition of a statistical space mapping, while introducing the portable mapping concept for flexible model development for passive modeling. The portable mapping is a single-development-multiple-use versatile wrapper, such that after development it can be conveniently combined with any nominal model to form a set of statistical models of different speed and accuracy. This provides variety in model selection for different design needs. To further reduce modeling cost, i.e., the simulation time required for model data generation, a smart sampling technique is used to achieve better sampling fidelity with smaller sample size. The portable statistical mapping technique is demonstrated through modeling a transmission line and a spiral inductor. © 2006 IEEE.
Sahu A, Grayczyk B, Almalkawi M, Devabhaktuni V, Aaen P (2014) High-Q spiral inductors with multilayered split-ring resonator (SRR) patterned ground shields, IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) pp. 346-347
© 2014 IEEE.This paper demonstrates a new concept of multilayered patterned ground shield (PGS) for improving Q-factor of a Si-based spiral inductor. The impact of left-handed behavior of complementary split ring resonator (CSRR) and split ring resonator (SRR) patterns to realize a high inductance in the ground shield is explained through an equivalent circuit model. The proposed two layer patterned ground shield is shown to improve the Q-value of on-chip spiral inductors by 23.7%.
Everett JP, Kearney MJ, Snowden CM, Rueda H, Johnson EM, Aaen PH, Wood J (2012) Process-orientated physics-based modeling of microwave power transistors: Small-and large-signal characterization, IEEE MTT-S International Microwave Symposium Digest IEEE
The coupling between charge transport, heat and energy flow required to model high frequency power devices is developed in the context of a computationally efficient physics-based model, which has been successfully applied to microwave laterally diffused MOS transistors. The accurate prediction of small-and large-signal microwave characteristics, and the physical insight gained, can be used in the process-orientated optimization and process sensitivity analysis of LDMOS power FETs. The charge-based model is well-suited to non-linear CAD implementation for applications such as power amplifier design. © 2012 IEEE.
Aaen PH, Zhang L, Kim K (2016) Characterization and Modeling of Frequency Dispersion in RF LDMOS Transistors, Proceedings of EuMW 2016
This paper characterises the effects of frequency
dispersion in laterally diffused metal-oxide semiconductor (LDMOS)
from pulsed-S-parameter measurement. Using the calculated
high-frequency drain current from measured data, we
demonstrate that length of the lightly doped drain extension is
directly proportional to the amount of current collapse at high
frequency. To capture the frequency dispersion in a nonlinear
model, a frequency-domain mapping technique is proposed to
allow us to augment quasi-static nonlinear electrothermal models.
The importance of including the dispersiveness is demonstrated
through comparing a standard quasi-static model, the newly
augmented model and on-wafer load-pull measurements. For a
5-mm, 500 m unit-gate-width transistor, we demonstrate that
the quasi-static model over predicts the drain efficiency during
large signal drive at P3dB by 9%. The new augmented model is
able to predict the efficiency within 2% of the measured value.
Bridges D, Wood J, Guyonnet M, Aaen PH (2008) A nonlinear electro-thermal model for high power RF LDMOS transistors, IEEE MTT-S International Microwave Symposium Digest pp. 475-478
A new nonlinear, charge-conservative, dynamic electro-thermal compact model for LDMOS RF power transistors is described in this paper. The transistor is characterized using pulsed I-V and S-parameter measurements, to ensure isothermal conditions. The intrinsic model current and charge sources are obtained by integration of the real and imaginary components, respectively, of the small-signal Y-parameters: this yields a charge-conservative model by design. A thermal sub-circuit is used to introduce dynamic thermal dependence, and thermal threshold voltage shift is built in. DC and large-signal validation of the model is presented. © 2008 IEEE.
Dehghan N, Porch A, Cripps SC, Aaen PH (2011) A novel high resolution E-field microscope system with applications in HPA diagnostics, 78th ARFTG Microwave Measurement Conference: High Power RF Measurement Techniques, ARFTG 2011 IEEE
A new type of high resolution E-field microscope system is described. The system is based on a novel design of an active E-field probe (EFP) probe, which is both nonintrusive and displays high spatial resolution. This paper focuses on the construction and spatial resolution of the probe, which shows significant evolution from that previously reported [1], and some measurements on passive structures which indicate that features smaller than 100 microns can be individually resolved. The probe construction lends itself to further improvements in spatial resolution. Measurement results are presented which demonstrate the high resolution of the probe, and its potential utility in measuring waveforms with high spatial resolution at individual points on microwave circuits, discrete devices, and integrated circuits. © 2011 IEEE.
Sheikh A, Roff C, Benedikt J, Tasker PJ, Noori B, Wood J, Aaen PH (2009) Peak class F and inverse class F drain efficiencies using si LDMOS in a limited bandwidth design, IEEE Microwave and Wireless Components Letters 19 (7) pp. 473-475
This paper compares two popular high power, high efficiency modes of operation, class F and inverse class F, and assesses the peak obtainable drain efficiencies when using Si LDMOS devices in a limited bandwidth design. Optimum class F and inverse class F conditions are presented using active harmonic load-pull measurements, and it was found that a higher drain efficiency was achieved in the class F configuration. This result is due to the limitations imposed by the soft voltage breakdown occurring due to the extended voltage swings inherent to inverse class F, as a consequence generating unwanted current content during the off cycle. This significantly reduces the peak measured efficiency using Si LDMOS devices when implementing an inverse class F design with a drain bias of 28 V. By reducing the drain bias to 18 V, to accommodate the voltage extension of inverse class F, it became possible to achieve peak measured efficiencies much closer to what theory predicted. © 2006 IEEE.
Wood J, Aaen PH, Bridges D, Lamey D, Guyonnet M, Chan DS, Monsauret N (2009) A nonlinear electro-thermal scalable model for high-power RF LDMOS transistors, IEEE Transactions on Microwave Theory and Techniques 57 (1) pp. 282-292 IEEE
A new nonlinear charge-conservative scalable dynamic electro-thermal compact model for laterally defused MOS (LDMOS) RF power transistors is described in this paper. The transistor is characterized using pulsed I-V and S-parameter measurements, to ensure isothermal conditions. A new extrinsic network and extrinsic parameter-extraction methodology is developed for high-power RF LDMOS transistor modeling, using manifold deembedding by electromagnetic simulation, and optimization of the extrinsic network parameter values over a broad frequency range. The intrinsic model comprises controlled charge and current sources that have been implemented using artificial neural networks, designed to permit accurate extrapolation of the transistor's performance outside of the measured data domain. A thermal sub-circuit is coupled to the nonlinear model. Large-signal validation of this new model shows a very good agreement with measurements at 2.14 GHz. © 2008 IEEE.
Hart P, Wood J, Noori B, Aaen P (2007) Improving loadpull measurement time by intelligent measurement interpolation and surface modeling techniques, 2006 67th ARFTG Microwave Measurements Conference - Measurements and Design of High Power Devices and Systems pp. 69-72 IEEE
In this paper we show how a thin-plate spline approximation can be used to generate a model of the measured response surface of a load-pull measurement over a much-reduced number of impedance points with no significant loss of accuracy. Further, interpolation between these model surfaces is possible, generating accurate drive-up characteristics. This has enabled accurate load-pull characterizations to be made in a fraction of the usual time.
Aaen PH, Plá JA, Balanis CA (2004) Increased feedback due to package mounting, IEEE Topical Meeting on Electrical Performance of Electronic Packaging pp. 49-52
The affect of the ground step discontinuity created by a difference in package and printed circuit board (PCB) thickness was studied. It is observed that the step in the reference conductor can be represented by a series inductance and its value depends on the height of the step and the width of the transmission line above it. The overall circuit affects for a packaged transistors were simulated with commercially available electromagnetic 2D and 3D CAD tools. The results show that the discontinuity creates an inductive feedback path around the package.
Everett JP, Kearney MJ, Rueda HA, Johnson EM, Aaen PH, Wood J, Snowden CM (2011) Fast physical models for Si LDMOS power transistor characterization, IEEE MTT-S International Microwave Symposium Digest
A new quasi-two-dimensional (Q2D) model is described for microwave laterally diffused MOS (LDMOS) power transistors. A set of one-dimensional energy transport equations are solved across a two-dimensional cross-section in a "current-driven" form. This process-oriented nonlinear model accounts for thermal effects, avalanche breakdown and gate conduction. It accurately predicts DC and microwave characteristics as demonstrated by comparison with measured DC characteristics, transconductance, forward gain, S21, and large-signal gate and drain charges for a LDMOS transistor. The model is fast, taking less than 30 ms to extract a 50 point DC I DS-VDS characteristic and less than 5 ms to produce S-parameters at a single frequency. © 2011 IEEE.
Aaen PH, Wood J, Li Q, Mares E (2010) Thermal resistance modeling for the electrothermal layout of high-power RF transistors, IEEE MTT-S International Microwave Symposium Digest pp. 1672-1675 IEEE
This paper demonstrates a practical approach to developing a geometrically scalable thermal resistance model to optimize layout for improved electrical performance of highpower RF transistors. The model is developed using finite element-based simulations, which show very good agreement with measured results. The proposed modeling methodology precomputes simulations over all possible layout considerations and the individual elements of the thermal resistance matrices are automatically approximated by thin-plate splines. This approach produces a model for use within a circuit simulator with virtually no overhead. We are able to scale the model up to 60 mm with less than than 2% error in the maximum predicted temperature rise. © 2010 IEEE.
Aaen PH, Plá JA, Balanis CA (2006) Modeling techniques suitable for CAD-based design of internal matching networks of high-power RF/microwave transistors, IEEE Transactions on Microwave Theory and Techniques 54 (7) pp. 3052-3058
A scalable and accurate simulation technique to be used for the computer-aided design (CAD) of matching networks employed within high-power RF transistors is presented. A novel measurement methodology is developed and utilized during the validation of the proposed analysis approach. Appropriate segmentation techniques were developed, which are consistent with the design approach of the high-power transistor, that take into account the overall complexity of the internal match of most modern RF high-power transistors, while preserving important electromagnetic interactions. By being able to properly decouple the linear portion of the overall packaged transistor model, an objective accuracy assessment via the comparison of measured versus simulated results of the internal matching network was accomplished. The level of accuracy obtained provides credence to the idea of a full CAD-driven design process of the internal match of high-power RF transistors. © 2006 IEEE.
Everett JP, Kearney MJ, Rueda H, Johnson EM, Aaen PH, Wood J, Snowden CM (2011) A Quasi-Two-Dimensional Model for High-Power RF LDMOS Transistors, IEEE TRANSACTIONS ON ELECTRON DEVICES 58 (9) pp. 3081-3088 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Aaen PH, Wood J, Bridges D, Zhang L, Johnson E, Barbieri T, Pla J, Snowden CM, Everett JP, Kearney MJ (2012) Multi-physics modeling of high-power microwave transistors, IEEE MTT-S International Microwave Symposium Digest IEEE
In this paper, we present a multi-physics approach for the simulation of high-power microwave transistors in which electromagnetic, thermal, and nonlinear transistor models are linked together within a harmonic-balance circuit simulator. This approach is used to analyze an LDMOS transistor operating at 2.14 GHz. The total gate width of the die is 102 mm, and the die is placed in a ceramic package and connected using bond-wire arrays at gate and drain. The effects of three different gate bond-pad metallization on the transistor efficiency are studied. Plots of the spatial distribution of the drain efficiency, and time-domain current and voltage provide a unique insight and understanding of the behaviours induced by the different bond-pads. © 2012 IEEE.
Wood J, Aaen PH, Piá JA (2008) Characterization and modeling of LDMOS power FETs for RF power amplifier applications, 2008 IEEE Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systms - Digest of Papers, SiRF pp. 134-138 IEEE
In this review we present a measurement-based approach to the creation of a successful circuit model of a high-power RF FET. We describe some of the measurement challenges that we face in the characterization and validation of the FET model, and our approach to their solution. We also outline some of the simulation and modeling techniques that are used in the construction of the complete transistor model. The model itself is fully nonlinear, with a self-consistent dynamic electrothermal component, and includes the in-package matching and package components, which are derived from electro-magnetic simulations. © 2008 IEEE.
Alshamaileh KA, Almalkawi MJ, Junuthula RR, Devabhaktuni VK, Aaen PH (2015) ANN-based modeling of compact impedance-varying transmission lines with applications to ultra-wideband Wilkinson power dividers, International Journal of RF and Microwave Computer-Aided Engineering
© 2015 Wiley Periodicals, Inc. The modeling of the physical and electrical characteristics of microstrip non-uniform transmission lines (NTLs) utilizing artificial neural networks (ANNs) is investigated. The fundamental equations and constraints for designing variable impedance transmission lines are first presented. Then, a proof-of-concept example of a compact non-uniform matching transformer and the counterpart modeled version is elaborated for source and load impedances Zs and Zl, respectively, at 0.5 GHz. For comparison purposes, weights and biases of the proposed ANN are established with three different training techniques; namely: backpropagation (BP), Quasi-Newton (QN), and conjugate gradient (CG); at which the ABCD matrix, impedance variations, input port matching (S11), and transmission parameter (S21) are set as benchmarks to examine the validity of the trained model. The concept is then extended to model a NTL ultrawideband (UWB) Wilkinson power divider (WPD) with three resistors for improved isolation. S-parameters derived from the trained ANN outputs are close to those obtained by the traditional time-consuming optimization procedure, and show input and output ports matching and isolation of below -10 dB, and acceptable values of transmission parameters over the 3.1 GHz to 10.6 GHz band. The resulting models outperform traditional optimizations in terms of simulation time and reserved resources with comparable accuracy.
Alshamaileh KA, Almalkawi MJ, Junuthula RR, Devabhaktuni VK, Aaen PH (2015) ANN-based modeling of compact impedance-varying transmission lines with applications to ultra-wideband Wilkinson power dividers, International Journal of RF and Microwave Computer-Aided Engineering 25 (7) pp. 563-572
© 2015 Wiley Periodicals, Inc.The modeling of the physical and electrical characteristics of microstrip non-uniform transmission lines (NTLs) utilizing artificial neural networks (ANNs) is investigated. The fundamental equations and constraints for designing variable impedance transmission lines are first presented. Then, a proof-of-concept example of a compact non-uniform matching transformer and the counterpart modeled version is elaborated for source and load impedances Zs and Zl, respectively, at 0.5 GHz. For comparison purposes, weights and biases of the proposed ANN are established with three different training techniques; namely: backpropagation (BP), Quasi-Newton (QN), and conjugate gradient (CG); at which the ABCD matrix, impedance variations, input port matching (S11), and transmission parameter (S21) are set as benchmarks to examine the validity of the trained model. The concept is then extended to model a NTL ultrawideband (UWB) Wilkinson power divider (WPD) with three resistors for improved isolation. S-parameters derived from the trained ANN outputs are close to those obtained by the traditional time-consuming optimization procedure, and show input and output ports matching and isolation of below -10 dB, and acceptable values of transmission parameters over the 3.1 GHz to 10.6 GHz band. The resulting models outperform traditional optimizations in terms of simulation time and reserved resources with comparable accuracy.
Aaen PH, Plá JA, Balanis CA (2005) On the development of CAD techniques suitable for the design of high-power RF transistors, IEEE Transactions on Microwave Theory and Techniques 53 (10) pp. 3067-3074
A full-wave modeling procedure was developed to simulate the package, bonding wires, and MOS capacitors used in the design of matching networks found within RF/microwave power transistors. The complex packaging environment was segmented into its constituent components and simulation techniques were developed for each component, as well as the inter-element coupling. An S-parameter test fixture and package was developed that permits measurements of these types of devices. The simulation and measurement procedures were used to model various circuits. Measured S-parameters and those obtained using the full-wave methodology were in good agreement. Simulation results using an inductance-only bonding-wire model were performed and differences between the S-parameters were observed. A detailed examination of the loss introduced by the matching network was performed and simulations and measurements matched closely. © 2005 IEEE.
Mareddy L, Almalkawi M, Devabhaktuni V, Vemuru S, Zhang L, Aaen PH (2012) Gradient based reverse ANN modeling approach for RF/microwave computer aided design, European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 7th European Microwave Integrated Circuits Conference, EuMIC 2012 pp. 246-249 IEEE
In this work, a new gradient based reverse modeling approach employing Artificial Neural Networks (ANNs) for systematic RF/microwave modeling is introduced. This approach is particularly suited to modeling scenarios, where standard ANN multi-layer perceptron (MLP) fails to deliver a satisfactory model. The proposed approach detects the simplest input-output relationship inherent to the modeling problem, which we term as the reverse model as compared to the original model (i.e., the modeling problem using standard ANN model). This reverse model is short-listed from a pool of candidate models obtained by systematically reversing the input-output variables of the original modeling problem, while retaining the ANN's structural simplicity. The proposed reverse and the not-so-Accurate original models complement each other to yield accurate models. The advantages of this approach are demonstrated via modeling transmission lines and spiral inductors. © 2012 European Microwave Assoc.
Sheikh A, Roff C, Benedikt J, Tasker PJ, Noori B, Aaen P, Wood J (2008) Systematic waveform engineering enabling high efficiency modes of operation in Si LDMOS at both L-band and S-band frequencies, IEEE MTT-S International Microwave Symposium Digest pp. 1143-1146 IEEE
This paper demonstrates that by robust waveform engineering it is possible for high power Si LDMOS to achieve very high efficiency at frequencies up to 2.1GHz. Class F amplifier operation was realized in a 5W LDMOS device by the successful application of robust waveform engineering procedures; undertaken at the current generator plane. The peak power added efficiency was found to be 78% at 0.9GHz and 77% at 2.1GHz. In both cases the RF waveforms were optimized in terms of the gate voltage, fundamental and harmonic impedances. The main difference at 2.1GHz was the change in fundamental impedance to a more reactive impedance to compensate for the dynamic device output capacitance. To the authors' knowledge this is the highest efficiencies reported in the literature for Si LDMOS devices at 2.1GHz. © 2008 IEEE.
Barbieri T, Aaen PH, Noori B (2013) Removal of measurement artifacts present in high-power RF transistor loadpull test-fixtures, 81st ARFTG Microwave Measurement Conference: Metrology for High Speed Circuits and Systems, ARFTG 2013
In this paper we investigate the effect of a discontinuity, at the measurement reference plane, on loadpull measurements of high-power RF transistors. The discontinuity is created by transition from the microstrip transformers on the printed-circuit board of the test-fixture to the packaged transistor. Our measurements indicate that the discontinuity does not change the peak performance of a packaged transistor but it can significantly alter the impedances at which this performance occurs. Through a straight-forward electromagnetic simulation we are able to characterize the discontinuity and remove it from measurement. © 2013 IEEE.
Aaen PH, Plá JA, Wood J (2007) Modeling and characterization of RF and microwave power fets, pp. 1-362
© Cambridge University Press 2007 and Cambridge University Press, 2009.This 2007 book is a comprehensive exposition of FET modeling, and is a must-have resource for seasoned professionals and new graduates in the RF and microwave power amplifier design and modeling community. In it, you will find descriptions of characterization and measurement techniques, analysis methods, and the simulator implementation, model verification and validation procedures that are needed to produce a transistor model that can be used with confidence by the circuit designer. Written by semiconductor industry professionals with many years' device modeling experience in LDMOS and III-V technologies, this was the first book to address the modeling requirements specific to high-power RF transistors. A technology-independent approach is described, addressing thermal effects, scaling issues, nonlinear modeling, and in-package matching networks. These are illustrated using the current market-leading high-power RF technology, LDMOS, as well as with III-V power devices.
Everett JP, Kearney MJ, Snowden CM, Rueda HA, Johnson EM, Aaen PH, Wood J (2011) Optimization of LDMOS power transistors for high power microwave amplifiers using highly efficient physics-based model, European Microwave Week 2011: "Wave to the Future", EuMW 2011, Conference Proceedings - 6th European Microwave Integrated Circuit Conference, EuMIC 2011 pp. 41-44
A new quasi-two-dimensional physical model is described for microwave LDMOS power transistors. This nonlinear, process-oriented, model accounts for avalanche breakdown, hot carriers and process variations, and accurately predicts DC and microwave characteristics. The model has been applied to the optimization of LDMOS structures and shows good agreement over a wide range of structural variations. It is over three orders of magnitude faster than conventional two-dimensional physical models whilst maintaining a high level of accuracy, which makes it ideally suited to microwave CAD. © 2011 EUROPEAN MICROWAVE ASSOC.
Noori B, Hart P, Wood J, Aaen PH, Guyonnet M, Lefevre M, Plá JA, Jones J (2007) Load-pull measurements using modulated signals, Proceedings of the 36th European Microwave Conference, EuMC 2006 pp. 1594-1597 IEEE
In this paper we report a method of applying digitally modulated signals to an RF power transistor in a load-pull system. This methodology ensures that the transistor experiences realistic thermal conditions, as well as realistic electrical conditions during test. The measured data is then sliced at constant value of CCDF enabling meaningful performance comparisons to be made between devices and technologies. © 2006 EuMA.
Kabir H, Zhang L, Yu M, Aaen PH, Wood J, Zhang QJ (2010) Smart modeling of microwave devices, IEEE Microwave Magazine 11 (3) pp. 105-118
An overview of neural network-based modeling techniques and their applications in microwave modeling and design is presented. The neural network represent RF/microwave components with the help of training data that are pairs of model input-output (IO) data generated from detailed microwave simulation or measurement. Neural networks have significant advantages over other techniques for multidimensional function approximation as they permit a compact representation of a multidimensional function, requiring minimal storage of coefficients and being very efficient to evaluate. The neural network can produce a parametric model by exploiting existing microwave knowledge in the form of empirical/analytical/equivalent model during neural network development. Neural network maps an existing model to match a new device with a technique called Neuro-Space Mapping (Neuro-SM).
Wood J, LeFevre M, Runton D, Nanan JC, Noori BH, Aaen PH (2006) Envelope-domain time series (ET) behavioral model of a Doherty RF power amplifier for system design, IEEE Transactions on Microwave Theory and Techniques 54 (8) pp. 3163-3171
In this paper, we present an envelope-domain behavioral model of a high-power RF amplifier. In this modeling approach, we use the signal envelope information, and the behavioral model is generated using an established nonlinear time-series approach to create a time-domain model that operates in the envelope or signal domain. We have generated a model of a 200-W Doherty amplifier from measured IQ data taken using a wideband code-division multiple-access excitation; the amplifier was driven from the linear regime into saturation. The time-series model was created using a time-delay embedding identified from auto-mutual information analysis, and an artificial neural network was used to fit the multivariate transfer function. The model has been validated using measured and simulated data, and it has been used in the development of a system-level design of a digital pre-distorter. © 2006 IEEE.
Sahu A, Devabhaktuni V, Lewandowski A, Barmuta P, Wallis TM, Shkunov M, Aaen PH (2015) Microwave Characterization of Ink-Jet Printed CPW on PET Substrates, 2015 86TH ARFTG MICROWAVE MEASUREMENT CONFERENCE IEEE
Stant L, Aaen PH, Ridler N (2016) Evaluating Residual Errors in Waveguide Network Analysers from Microwave to Submillimetre-wave Frequencies, IET Microwaves, Antennas and Propagation 11 (3) pp. 324-329 IET
Vector network analysers (VNA) are used extensively for measurements that are made at frequencies ranging from a few kilohertz to at least one terahertz. At radio and microwave frequencies, there are well-established methods for assessing the quality and confidence of these measurements, when they are made in coaxial lines. These methods are usually based on determining the size of residual errors that remain in the VNA after calibration. To date, the performance of these methods has not been investigated in rectangular waveguide, and, at millimetre- and submillimetre-wave frequencies. This paper investigates the application of one of these techniques for waveguide measurements at microwave, millimetre- and submillimetre-wave frequencies. Typical values of residual errors obtained over these frequency ranges are given. These values are considered representative and so can be used by other users of waveguide VNAs to compare with values obtained on their own systems, therefore helping to verify the performance of their systems.
Hussein O, Al shamaileh K, Devabhaktuni V, Aaen PH (2017) Wideband Impedance-varying N-way Wilkinson Power Divider/Combiner for RF Power Amplifiers, Proceedings of 88th ARFTG Microwave Measurement Symposium
We propose a compact wideband multi-way power divider/combiner with planar structure for applications to RF power amplifiers (PAs). Uniform transmission lines in the conventional divider are replaced with non-uniform transmission lines (NTLs), which are governed by a truncated Fourier series. An optimization-driven framework is employed in even-mode analysis to obtain the coefficients of the NTLs considering predefined operating bands, whereas three isolation resistors are optimized in the odd-mode analysis to achieve optimal isolation and output port matching over the design bandwidth. For verification purposes, a 4?10 GHz 3-way divider is simulated, and measured. Simulations and measurements are in close proximity and show input/output ports matching of better than ?10 dB and transmission of ?4.9 ±1 dB across the design bandwidth.
Votsi H, Roch-Jeune I, Haddadi K, Li C, Dambrine G, Aaen PH, Ridler N (2017) Development of a Reference Wafer for On-Wafer Testing of Extreme Impedance Devices, Proceedings of 88th ARFTG Microwave Measurement Symposium
This paper will describe the design, fabrication and testing of an on-wafer substrate that has been developed specifically for measuring extreme impedance devices using an on-wafer probe station. Such devices include Carbon Nano-Tubes (CNTs) and structures based on graphene which possess impedances in the k© range and are generally realised on the nano-scale rather than the micro-scale that is used for conventional on-wafer measurement. These impedances are far removed from the conventional 50 © reference impedance of the test equipment. The on-wafer substrate includes methods for transforming from the micro-scale to the nano-scale and reference standards to enable calibrations for extreme impedance devices. The paper includes typical results obtained from the designed wafer.
Sahu A, Devabhaktuni V, Mishra R, Aaen PH (2015) Recent Advances in Theory and Applications of Substrate-Integrated Waveguides: A Review, International Journal of RF and Microwave Computer-Aided Engineering 26 (2) pp. 129-145 Wiley
The use of substrate integrated waveguides (SIW) for microwave and millimeter wave integrated components has increased dramatically over the last decade. They mimic the performance of conventional metallic waveguides and they are fabricated using printed circuit boards using the top and bottom metallisation with two rows of vias forming the side walls. This creates a low profile, compact, and light weight alternative to conventional metallic waveguides, and they allow a direct interconnection with printed circuit boards and active components. This paper reviews the fundamental theory, documents the research that has been performed over the past decade, and summarises progress up to the recent state-of-the-art including novel SIW structures for passive circuits and antennas as well as new applications for reconfigurable and printed circuits using SIW technology.
Votsi Haris, Li C, Aaen Peter H, Ridler NM (2017) An Active Interferometric Method for Extreme Impedance On-Wafer Device Measurements, IEEE Microwave and Wireless Components Letters. 27 (11) pp. 1034-1036 IEEE
Nano-scale devices and high power transistors
present extreme impedances, which are far removed from the
50-© reference impedance of conventional test equipment,
resulting in a reduction in the measurement sensitivity as
compared with impedances close to the reference impedance. This
letter describes a novel method based on active interferometry
to increase the measurement sensitivity of a VNA for measuring
such extreme impedances, using only a single coupler. The
theory of the method is explained with supporting simulation.
An interferometry-based method is demonstrated for the
first time with on-wafer measurements, resulting in an
improved measurement sensitivity for extreme impedance device
characterization of up to 9%.
Sahu A, Aaen P, Lewandowski A, Shkunov M, Rigas G, Blanchard P, Wallis T, Devabhaktuni V (2017) Robust Microwave Characterization of Inkjet Printed Coplanar Waveguides on Flexible Substrates, IEEE Transactions on Instrumentation & Measurement 66 (12) pp. 3271-3279 IEEE
In this paper, we propose a robust microwave
characterization of inkjet printed components on flexible substrates,
which aim at measuring the material properties of
silver nanoparticle inks and the supporting dielectric spacer
employed during measurements. Starting with propagation constant
extracted from multiline thru-reflect-line calibration with
coplanar waveguide (CPW) standards and then proceeding with
finite element modeling of CPWs, the proposed technique can
dynamically produce an interpolated search space by automatic
driving of simulation tools. In the final stage, the algorithm
utilizes a least-square optimization routine to minimize the
deviation between model and measurements. Our technique
significantly reduces the computing resources and is able to
extract the material parameters using even a nominal ink profile.
Characteristic impedances for CPWs are extracted using series
resistor measurements from 10 MHz to 20 GHz. It is also
shown that the proposed characterization methodology is able
to detect any changes in material properties induced by changes
in fabrication parameters such as sintering temperature. Ink
conductivities of approximately 2.973×10^7 S/m and spacer
dielectric constant of 1.78 were obtained for the inkjet printed
CPWs on PET. In addition, the inkjet printed CPWs sintered at
170°C and 220°C on Kapton had conductivities of 0.187×10^7 and 0.201×10^7 S/m respectively. We verified our technique by
measuring the material parameters with conventional approach.
Goss Tristan JD, Aaen Peter (2018) Behavioural Modelling for Adaptive Array Systems Incorporating High-Power Amplifier Nonlinearities, EuCAP 2018 - The 12th European Conference on Antennas and Propagation, London, England European Association on Antennas and Propagation
We develop a novel method for the behavioural
modelling of adaptive array systems (AASs) incorporating high-
power amplifier (HPA) nonlinearities. The model is motivated
by the need to better define the spatial and spectral interference
profile of AASs. We provide a simulated proof of concept as a
precursor to experimental validation. In our demonstration, the
model is identified using simulated near-field measurements made
while the antenna?s input channels are simultaneously undergoing
a representative excitation. These measurements are used to
identify a large number of memory polynomials (MPs) which
characterise the transfer function from the antenna inputs to the
near-field. We then use the array of MPs and a near-field to far-
field transformation to obtain the far-field pattern of the antenna
for arbitrary input. We show the impact of antenna element HPA
nonlinearities on the far-field pattern, and our ability to predict
them via the developed model.
Matei Cristian, Aaen Peter, Kending D (2017) High-Resolution Thermoreflectance Imaging of GaN
Power Microwave Transistors. Invited paper.,
ARMMS RF & MICROWAVE SOCIETY
The ever-increasing power density of semiconductors used in monolithic microwave integrated circuits (MMICs) and power amplifiers (PAs) mandates good thermal management and accurate temperature measurements are needed to study device reliability, assess temperature gradients, and to validate nonlinear electrothermal model performance.

Thermoreflectance based temperature measurements have been recently applied to high-power microwave semiconductors. The technique determines the temperature by measuring the change in reflectance from a surface due to changing in the index of refraction of the sample. Since the measurement technique uses visible light, thermoreflectance imaging can achieve a spatial resolution of 290 nm and sub-nanosecond temporal resolution over a wide field of view. This makes the method well suited to study the thermal dynamics within these transistors.

This presentation will review the capabilities of thermoreflectance measurement, explain the theory behind the thermoreflectance phenomenon, and demonstrate the usefulness of the method and the insights that can be gained by examining several recent measurements.

Votsi Haris, Aaen Peter, Gillespie Sean, Mirkhaydarov Bobur, Shkunov Maxim, Young P. R. (2018) Modelling of Solution Processed Indium Arsenide Nanowire Microwave Switches, Proceedings of International Microwave Symposium 2018 (IMS2018) Institute of Electrical and Electronics Engineers (IEEE)
This paper presents the modelling of a coplanarwaveguide
bottom-gated FET switch using indium-arsenide
nanowires. The nanowires have been included on the switch
using dielectrophoresis, which is a solution processable
technique. This is a necessary first step towards developing
a fully printable switch on a flexible substrate, for low cost
microwave devices, built using additive manufacturing methods.
The measured S-parameters show the switching capabilities of
the device with an insertion loss of 9 dB, when the switch is
open (gate voltage e 60 V). The development of a distributed
circuit model that matches the measured data is described,
alongside the calculated network parameters used to represent
the coplanar-waveguide and the nanowires. The model fits the
measured results within 8%, making it suitable for inclusion in
a CAD based circuit simulator.
Zhang Lei, Aaen Peter, Kim Kevin, Rueda Hernan (2018) Non-Quasi-Static Large-Signal Model for RF LDMOS Power Transistors, Proceedings of International Microwave Symposium 2018 (IMS2018) Institute of Electrical and Electronics Engineers (IEEE)
In this paper, we propose a non-quasi-static large-signal
model to capture the high-frequency dispersion exhibited by
laterally diffused metal-oxide semiconductor (LDMOS) devices.
We show that industry-standard nonlinear large-signal models for
LDMOS based on quasi-static assumptions are not sufficient for
high-efficiency designs at frequencies higher than 2 GHz. This dispersive
behavior results from the combination of high-frequency
operation and the lengthened drain extension region that is needed
to support high-voltage operation. To improve the model accuracy,
higher-order current and charge components, which are directly
integrated from bias-dependent S-parameter data, are included
in the model. The non-quasi-static large-signal model improves
the efficiency and gain predictions by 10% and 0.5 dB at
3.5 GHz. These improvements in accuracy are essential for power
amplifier designers to achieve the performance targets necessary
for 4G and upcoming 5G designs.
This project was dedicated to the development of solution-processed nanomaterials-based high-performance field-effect transistors (FETs) suitable for a new application area of printed reconfigurable antennas. The focus of research was on implementing solution processed high electron mobility InAs nanowires (NWs) as semiconducting channel in field effect transistors. The key direction of this work was the development of InAs NWs FETs with a designated high frequency waveguide geometry to enable they operation as microwave switch elements.
Initially, InAs NW FETs were developed and tested in direct ? current mode to allow evaluation and extraction of key transistor performance parameters such charge carrier mobility, threshold, on/off ratio, transconductance, subthreshold swing, and on-channel resistance. The InAs NW were assembled from nanowire ?inks? in the FETs channel via electric -field assisted assembly technique, dielectrophoresis. Nanowires were directly incorporated in FETs with bottom-gate architecture on Si/SiO2 substrates, and with top-gate architecture on quartz substrates with polymeric gate dielectrics. Current-voltage characteristics were measured both in controlled dry nitrogen atmosphere and ambient environment, and demonstrated an instability of unprotected InAs NW in ambient air. Protection of nanowire channel with Al2O3 layers has resulted in significant improvement of device stability. Optimised InAs NW FET devices demonstrated electron mobility over 1000 cm2/Vs and on-off current ratios up to 1000.
Finally, a proof of principle for solution processed InAs NW field-effect transistors operating as microwave switches in 5-33GHz frequency range have been demonstrated. FET devices were implemented in co-planar waveguide (CPW) microwave transmission line geometry, providing efficient transmission or reflection of microwave signal. The FETs demonstrated high performance with transistor ON-state resistance as small as H50 © providing an excellent impedance match to that of microwave waveguide. Bringing FETs to the OFF state provided 1000 times resistance increase, resulting in FET microwave switch behaviour, characterised by ~10 dB change in scattering (S)-parameters, such as difference in transmission coefficient S21 between on/off switching states.
Urbonas Jonas, Vanaverbeke F, Kim K, Aaen Peter (2018) Electro-Optic Near Field Imaging of High-Power RF/Microwave
Transistors in Plastic Packages,
91st ARFTG Microwave Measurement Conference Proceedings IEEE
In this paper, through-plastic vector E-field measurements
of an LDMOS transistor in an over-molded plastic
package are presented. The measurement system uses a
commercially-available electro-optic system connected to an
NVNA with a comb generator to non-invasively measure the
phase-coherent multi-harmonic E-fields. The device is measured
in a load-pull measurement system, which is used to present
optimal source and load impedances to the transistor during
the multi-harmonic E-field measurements. All three E-field components
are measured at the fundamental (2.2 GHz) and two
harmonics at P1dB = 53.2 dBm.
The Joint Committee for Guides in Metrology (JCGM) publishes and maintains reference documents relating to general aspects in metrology. Working Group 1 of the JCGM is responsible for the Evaluation of Measurement Data series of documents that gives information for evaluating and expressing uncertainty in measurement. This paper compares several methods for evaluating measurement uncertainty that are described in these documents. Emphasis is given to situations where more than one input quantity is measured simultaneously. This leads to an investigation into how these methods perform when these quantities are high-frequency electromagnetic scattering parameters. It is shown that for measurements involving a large number of input quantities, such as those involving microwave scattering parameters, the required number of observations for the approach given in the GUM Supplements to work can be prohibitively large.
Gillespie Sean J., Root David E., Marcu Mihai, Aaen Peter (2018) Electrothermal X-Parameters for Dynamic Modeling of RF and Microwave Power Transistors, Proceedings of the 21st European Microwave Week (EuMW 2018) Institute of Electrical and Electronics Engineers (IEEE)
For the first time, this paper presents and validates
a novel extension of the X-parameter behavioral modeling
paradigm to include dynamic electro-thermal phenomena, a key
source of long-term memory affecting transistors. The dynamic
thermal X-parameter model (DTXM) adds a novel but straightforward
method to implement envelope domain sub-circuit in a
feedback loop around a conventional static X-parameter model,
enabling the simulation of modulated waveform-dependent
dynamic self-heating effects. The extended model is identified
from conventional CW or pulsed X-parameter measurements,
over a range of ambient temperatures. A re-referencing of the
extracted X-parameter data to the junction temperature is
performed, based on estimated or a calculated thermal resistance
and thermal capacitance. The model can also be generated in the
simulation environment starting from a dynamic electro-thermal
compact time-domain model. The DTXM accounts for thermallyinduced
asymmetry of intermodulation distortion products and
temperature hysteresis depending on the signal bandwidth.
Urbonas Jonas, Kim Kevin, Vanaverbeke Frederik, Aaen Peter (2018) An Electro-Optic Pulsed NVNA Load-Pull System
for Distributed E-field Measurements,
IEEE Transactions on Microwave Theory and Techniques 66 (6) pp. 2896-2903 IEEE
In this paper, a new combined electro-optic and
pulsed nonlinear vector network analyser-based load-pull measurement
system for distributed multi-harmonic electric field
measurements is presented. The system uses an external electrooptic
probe to measure cross-frequency phase-coherent multiharmonic
vector E-fields with an 8 µm spatial resolution and
20 MHz ? 20 GHz bandwidth. We demonstrate the performance
of the distributed phase-coherent E-field measurements of Ex,
Ey and Ez components with 3 harmonics above a commercially
available large periphery, packaged, laterally diffused metaloxide-semiconductor
(LDMOS) transistor. The transistor was
measured at 2.2 GHz under pulsed conditions with 10 µs pulse
and 10 % duty cycle, while outputting 55.1 dBm of power. The
measured electric fields of the operating transistor are animated
for the first time and reveal complex non-uniform operation at
harmonic frequencies
Urbonas Jonas, Kim Kevin, Aaen Peter H (2018) Direct E-field Measurement and Imaging of
Oscillations within Power Amplifiers,
IEEE Transactions on Instrumentation and Measurement IEEE
We present for the first time a measurement system
that is capable of directly detecting and identifying the
physical location of an oscillation within RF and microwave
power amplifiers. The method uses a combined external electrooptic,
non-linear vector network analyzer, and vector load-pull
measurement system, which allows the measurement of crossfrequency
phase-coherent multi-harmonic vector electric fields
above the transistor with an 8 ¼m spatial resolution and 20 MHz ?
40 GHz bandwidth. Raster scans above the amplifier allow the
time-domain electric fields to be animated and superimposed
on top of the amplifier image enabling immediate identification
of any oscillations by direct inspection. The method is first
demonstrated on a low power amplifier composed of two parallel
0.1-W pHEMT transistors that is intentionally designed to have
an odd-mode oscillation. The applicability of the method is
further demonstrated by measuring and animating in-package
parametric odd-mode oscillations within a 260-W laterally diffused
metal-oxide-semiconductor (LDMOS) transistor operating
at 2.2 GHz under pulsed RF conditions with 10 ¼s pulses and
10% duty cycle. The measurement and identification technique
is applicable to all semiconductor devices as the external electric
field is non-invasively measured above the amplifier.
Stant Laurence T., Salter Martin J., Ridler Nick M., Williams Dylan F., Aaen Peter H. (2018) Propagating Measurement Uncertainty to Microwave Amplifier Nonlinear Behavioral Models, IEEE Transactions on Microwave Theory and Techniques Institute of Electrical and Electronics Engineers (IEEE)
We propagate for the first time correlated measurement
uncertainties into a nonlinear behavioral model of a
millimeter-wave amplifier. We make use of the National Institute
of Standards and Technology Microwave Uncertainty Framework
to evaluate the uncertainties in large-signal electromagnetic wave
measurements of an amplifier, followed by the extraction of Xparameters
using an industry standard algorithm. This extracted
model is included as a component in a circuit simulator to evaluate
gain and efficiency incorporating measurement uncertainty.
Mirkhaydarov Bobur, Votsi Haris, Sahu Abhishek, Caroff Philippe, Young Paul R., Stolojan Vlad, King Simon, Ng Calvin C H, Devabhaktuni Vijaya, Tan Hoe H, Jagadish Chennupati, Aaen Peter, Shkunov Maxim (2018) Solution?Processed InAs Nanowire Transistors as Microwave Switches, Advanced Electronic Materials Wiley
The feasibility of using self?assembled InAs nanowire bottom?gated field?effect transistors as radio?frequency and microwave switches by direct integration into a transmission line is demonstrated. This proof of concept is demonstrated as a coplanar waveguide (CPW) microwave transmission line, where the nanowires function as a tunable impedance in the CPW through gate biasing. The key to this switching capability is the high?performance, low impedance InAs nanowire transistor behavior with field?effect mobility of H300 cm2 V?1 s?1, on/off ratio of 103, and resistance modulation from only 50 © in the full accumulation mode, to H50 k© when the nanowires are depleted of charge carriers. The gate biasing of the nanowires within the CPW results in a switching behavior, exhibited by a H10 dB change in the transmission coefficient, S21, between the on/off switching states, over 5?33 GHz. This frequency range covers both the microwave and millimeter?wave bands dedicated to Internet of things and 5G applications. Demonstration of these switches creates opportunities for a new class of devices for microwave applications based on solution?processed semiconducting nanowires.
Sahu Abhishek, Aaen Peter, Devabhaktuni Vijay K Advanced Technologies for Next-Generation RF Front-End Modules, International Journal of RF and Microwave Computer-Aided Engineering Wiley
The complexity of RF front-end (RFFE) modules of wireless devices has increased dramatically over the past decade. In order to meet the demands for future mobile communications, RFFEs will need to enable multiband for global roaming, and multi-mode to support multiple cellular modes, incorporate beamforming antennas, and operate at mmwave frequencies. To this end, this paper presents a summary of the recent progress in RF substrate technologies, waveguide architectures and multi-band design techniques for 5G RFFE modules, and summarizes the present and future challenges in RFFE module design.