Nonlinear Characterization of Wideband Microwave Devices and Dispersive Effects in GaN HEMTs
Doktorsavhandling, 2018

Measurements play a key role in the development of microwave hardware as they allow engineers to test and verify the RF performance on a system, circuit, and component level. Since modern cellular standards employ complex modulation formats with wider signal bandwidths to cope with the growing demand of higher datarates, nonlinear characterization using wideband stimuli is becoming increasingly important. Furthermore, III-N semiconductor technologies such as gallium nitride (GaN) are to a larger extent utilized to enable higher performance in microwave circuits. However, GaN is highly frequency-dispersive due to trapping phenomena and thermal effects. This thesis deals with the development of nonlinear measurement instruments as well as characterization of dispersive effects in GaN high-electron-mobility transistors (HEMTs).

A measurement setup for wideband, nonlinear characterization of microwave devices has been designed and verified. The setup allows for simultaneous acquisition of low-frequency and radio-frequency signals from DC up to 4~GHz through the use of wideband signal generators and measurement receivers. This enables measurement scenarios such as multi-band load-pull and large-signal characterization of IQ-mixers, which can give useful insight into how to optimize the performance in a RF transmitter.

Electrothermal characterization of GaN devices has been carried out using conventional measurement methods such as pulsed I-V, and it is shown that trapping phenomena and thermal effects due to self-heating or mutual coupling are challenging to separate. Multiple methods must be utilized to fully characterize both the large-signal and small-signal impact on device performance. A new characterization method has been developed, for extraction of thermal transfer functions between mutually coupled devices on e.g. a semiconductor wafer. The method does not require any DC-bias on the measured devices, which can potentially reduce the influence of trapping during characterization of thermal properties in materials.


dispersive effects

electron trapping

thermal coupling





Kollektorn, MC2
Opponent: Prof. Paul J. Tasker


Sebastian Gustafsson


Vector-corrected Nonlinear Multi-port IQ-mixer Characterization using Modulated Signals

IEEE MTT-S International Microwave Symposium Digest,; (2017)p. 1433-1436

Paper i proceeding

Wideband RF characterization setup with high dynamic range low frequency measurement capabilities

2016 87th ARFTG Microwave Measurement Conference,; (2016)

Paper i proceeding

An Oscilloscope Correction Method for Vector-Corrected RF Measurements

IEEE Transactions on Instrumentation and Measurement,; Vol. 64(2015)p. 2541-2547

Artikel i vetenskaplig tidskrift

Dispersive Effects in Microwave AlGaN/AlN/GaN HEMTs With Carbon-Doped Buffer

IEEE Transactions on Electron Devices,; Vol. 62(2015)p. 2162-2169

Artikel i vetenskaplig tidskrift

A Novel Active Load-pull System with Multi-Band Capabilities

81st ARFTG Microwave Measurement Conference,; (2013)

Paper i proceeding

Gustafsson, S., Bremer, J., Bergsten, J., Buisman, K., Malko, A., Grünenpütt, J., Madel, M., Blanck, H., Rorsman, N.,Thorsell, M. "Methods for Electrothermal Characterization of GaN HEMT Structures"

Measurement instruments are essential tools for engineers to be able to test and verify the performance of electrical circuits and systems before integration into a product. Development times of products can be shortened through rapid prototyping using models extracted from accurate measurements. This thesis deals with the development of measurement instruments and methods for characterization of nonlinear microwave devices.

Nonlinearities in microwave circuits can for example arise through intentional overdrive for high efficiency operation or due to non-idealities in components. Modern cellular standards such as 4G, and the upcoming 5G standard, use communication signals with wide bandwidths to allow for higher data throughput in the cellular networks. Therefore, distortion due to nonlinearities is of increasing importance to study using wideband signals. As such, a wideband nonlinear measurement setup has been designed and verified in this thesis.

Designing high performance circuits for next generation wireless applications also requires the utilization of semiconductors with better material properties compared to silicon, such as gallium nitride (GaN). With GaN, higher output powers at higher frequencies are possible to obtain, allowing for e.g. higher data rates at longer distances between the base station and cell phone. However, GaN suffers from performance-degrading effects such as electron trapping, which is a result of defects in the GaN material. In order to understand these effects, and to be able to optimize the GaN material, there is a need for measurements which can capture trapping phenomena in a methodical way. This thesis also deals with characterization of such phenomena.

The measurement instruments and methods developed in this thesis can aid in the understanding of nonlinear phenomena, enabling the design of high performance circuits for next generation wireless applications.




Nanovetenskap och nanoteknik




Annan elektroteknik och elektronik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4439


Chalmers tekniska högskola

Kollektorn, MC2

Opponent: Prof. Paul J. Tasker