Electro-thermal Investigation of Next Generation Wide Bandgap Electronics
Open Access
- Author:
- Chatterjee, Bikramjit
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 13, 2020
- Committee Members:
- Sukwon Choi, Dissertation Advisor/Co-Advisor
Sukwon Choi, Committee Chair/Co-Chair
Md Amanul Haque, Committee Member
Stephen P Lynch, Committee Member
Joan Marie Redwing, Outside Member
Daniel Connell Haworth, Program Head/Chair - Keywords:
- Thermography
Thermal Management
Raman
Thermoreflectance
Infrared
GaN
Gallium Oxide
HEMT
MODFET
Optical Metrology
Wide Bandgap Semiconductor Devices
Field Effect Transistors
AlGaN
Schottky Barrier Diode
Power Electronics
Thermal Transport
Irradiation - Abstract:
- Continuous push towards semiconductor devices with smaller size and higher performance have led to the maturation of silicon (Si)-electronics in an astounding speed during the last century. However, during the past two decades, Si-electronics have faced its material capability limit and therefore new base material systems are necessary to continue the advancement of semiconductor device technologies and the growth of the multibillion-dollar electronics industry. Wide bandgap (WBG) semiconductor devices based on gallium nitride (GaN) and silicon carbide (SiC) are being developed to replace Si-devices in high power, high frequency applications due to their superior material properties. Among GaN devices, heterostructure field effect transistors based on aluminum gallium nitride (AlGaN) and GaN heterojunction, also known as AlGaN/GaN high electron mobility transistors (HEMTs) have received particular interest from researchers due to their high voltage and high current carrying capabilities. From a thermal engineering point-of-view, self-heating of these devices is one of the main hindrances that cause performance degradation and device reliability problems. It has been demonstrated that device mean-time-to-failure is a strong function of device peak temperature and hence it is imperative to develop metrology techniques that can measure the device peak temperature as accurately as possible. A comprehensive, in-situ, non-invasive optical characterization suite has been used in this work, in conjunction with a fully coupled 3-D electro-thermal modeling scheme to measure the device surface temperature distribution and predict the device peak temperature. The bias dependent self-heating of AlGaN/GaN HEMTs was investigated with this modeling scheme as well as thermoreflectance thermal imaging technique and it was observed that under identical power dissipation levels, depending on device bias conditions, the device peak temperature and temperature distribution could be significantly different. Using a novel above bandgap illumination thermoreflectance thermal imaging measurement, GaN surface close to the device peak temperature location was probed to reveal the prevalence of sub-continuum scale thermal transport effects. This was further validated with a multiscale model based on Boltzmann transport equation that showed ~20% underestimation of device peak temperature as compared to a validated continuum scale thermal model. Considerable research and development work led the next-generation WBG GaN technology to the verge of commercialization. Now, generation-after-next ultra-wide bandgap (UWBG) Ga2O3 and AlGaN based devices are being considered to further advance the power sector forward by pioneers in the semiconductors device community by exploiting their superior electrical properties compared to GaN and SiC. While AlGaN based HEMTs can utilize the technological improvements of the GaN system as a convenient platform, the availability of low-cost native substrates makes Ga2O3 a very attractive material candidate to advance high power device technologies. Correlation between several electronic and thermal transport properties and device self-heating was evaluated based on AlGaN channel HEMTs with different Al mole fractions. It was observed that the relative temperature independence of thermal conductivity as well as mobility, and reduction in contact resistance with increasing temperature make high Al fraction AlGaN channel devices suitable for high temperature operations. However fabricating ohmic contacts become challenging as the semiconductor bandgap increased. This was observed to impact the heat generation distribution, and in turn, the temperature distribution across the HEMTs. This phenomenon was further investigated using a Ga2O3 Schottky diode. For the first time, cross-sectional Raman thermography was performed on a diode to understand the self-heating behavior. It was observed that heat is concentrated near the anode due to the large contact resistance. Experimental results were used to build a physics-based full-scale 3-D electro-thermal model to compare similar structures based on different materials. It was found that the temperature increase in Ga2O3 ¬devices were 5× higher than that in SiC devices due to the poor thermal conductivity of Ga2O3. This massive disadvantage in the heat dissipation capability is the biggest roadblock that the Ga2O3 technology faces. Both rigorous thermal characterization studies and development of effective thermal management schemes are required to enable the Ga2O3 material system reach its potential. In order to achieve this goal, passive and active thermal management solutions for Ga2O3 MOSFETs were studied using an electro-thermal model validated against experimental data. A top-side thermal management scheme that involves diamond integration was proposed for these devices to mitigate the intense self-heating effect.