Research Thrust 1: Electro-thermal analysis of ultra wide bandgap power electronic devices based on AlGaN, Ga2O3, and diamond.
Research Thrust 2: Radiation effects, reliability study, and thermal management of lateral GaN high electron mobility transistors.
Research Thrust 3: Electro-thermal analysis of vertical GaN power electronics.
Research Thrust 4: Thermal characterization of 2D layered materials and devices.
Research Thrust 5: Elctro-thermo-mechanical reliability of AlScN and PZT piezoMEMS.
Why is our research important? – For commercial and military power conversion and radio frequency (RF) applications, new base materials are being adopted to construct transistors and diodes with higher performance/efficiency and smaller size than conventional Si-based devices. Intense research efforts during the past decade led to successful development of wide bandgap (WBG) semiconductor devices based on SiC and GaN. We are focusing on “generation-after-next” ultra-wide bandgap (UWBG) devices based on AlGaN, β-Ga2O3, and diamond that can further push the performance limit beyond that for current state-of-the-art devices.
Which application areas will be revolutionized by using these materials and devices?
However, a critical challenge exists that hinders the successful transition to these new device technologies. Smaller size and higher power means substantially higher power density for individual devices. Then how high can the heat flux of a WBG or UWBG device reach?
Larger than that on the Sun’s surface!
Therefore, WBG and UWBG devices inevitably face a serious thermal issue. The following figure shows the significance and reality of thermal issues related with these ultra-high performance electronic devices.
Therefore, electro-thermal co-design is necessary to guarantee the success of emerging UWBG device technologies. We use our unique expertise in micro/nanoscale thermal characterization and multiphysics simulation to i) evaluate device self-heating, ii) design thermal management solutions, iii) understand failure mechanisms, and iv) devise new characterization techniques.
Here is a brief description of our optical thermography techniques:
Raman Thermometry: Works for semiconductor materials
- Measures frequency/linewidth of phonons that are translated into thermal information
- Ideal for measuring temperatures of semiconductor materials
- Sub-micron spatial resolution (< 0.5 µm)
- Steady-state as well as transient thermal measurement with a temporal resolution better than 15 ns is possible
- Ideal for studying lateral devices (e.g., AlGaN/GaN HEMT, MEMS, etc.)
Thermoreflectance Thermal Imaging: Best tool for metallization structures
- Exploits the change in material reflectivity due to temperature rise
- Ideal technique for assessing temperature of metals
- High spatial resolution (< 0.5 µm)
- Offers means to perform 50 ns range transient thermal analysis
- Ideal for studying vertical devices (e.g., p-i-n diodes, bipolar transistors, etc.)
Infrared (IR) Thermography: Gives fast/easy means to acquire qualitative temperature maps
- Most commonly used optical thermometry technique in industry
- Generates 2-D temperature images
- Based on black-body radiation to obtain device thermal profiles
- Spatial resolution: 2.7 µm
- Emissivity calibration and coating strategies are important in order to obtain quantitatively accurate results
Electrical Temperature Sensitive Parameter Based Thermometry: Used when optical access is limited
- Uses temperature sensitive electrical parameters such as mobility, threshold voltage, current gain, etc. to estimate the junction temperature rise in microelectronic devices
- Thermal information is extracted from standard or special current-voltage measurements
- Useful for qualitatively investigating fully packaged devices
We also utilize Raman spectroscopy and photoluminescence for local stress measurement (<0.5 µm lateral resolution) with variable depth resolution.
In the end, we perform multi-physics based simulation that links semiconductor device physics with thermo-mechanical phenomena. Simulations are performed both at the device and chip level.