The Penn State TCL aims to understand reliability physics of new device technologies and to offer thermal management solutions to overcome such barriers.
Why is our research so important? – For commercial and military power conversion and radio frequency (RF) applications, device engineers leading the research field are employing new base materials to construct higher performance transistors and diodes that are smaller in size and more efficient than conventional silicon (Si) based devices. Wide bandgap semiconductors (SiC and GaN) are used in current state-of-the-art systems. Now TCL is focusing on the generation-after-next ultra-wide bandgap devices based on AlGaN, β-Ga2O3, and diamond.
Where do you expect these materials/devices will used?
OK. Then what’s the problem with these cool device technologies? Why do electrical engineers need our (your) help? Smaller size and higher power means…Yes, higher heat flux! But how high is the heat flux for individual wide bandgap or ultra-wide bandgap devices?
Larger than that on the Sun’s surface!
Remember, the motivation to advance wide bandgap (GaN, SiC) devices to ultra-wide bandgap parts was to further reduce the size and increase the power handling capability. So things will get hot…really hot which is not a good idea. The following figure shows the significance and reality of the thermal issues related with these ultra-high performance electronic devices.
Different from the role thermal engineers played during the design process of conventional semiconductor devices, we, electro-thermal engineers, are the ones who will contribute to the realization of electro-thermal co-design. We use our unique expertise in multi-physics simulation and micro-/nano-scale optical thermography to investigate device self-heating, design thermal management solutions, understand electro-thermo-mechanical failure mechanisms, and devise new thermal characterization techniques.
Here is a brief description of TCL’s 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 100 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 150 ns range (down to 800 ps) 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 information
- 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
TCL utilizes Raman spectroscopy and photoluminescence for also local stress measurement (<0.5 µm lateral resolution) with variable depth resolutions.
We perform multi-physics based simulation linking semiconductor device physics (TCAD modeling) with thermo-mechanical phenomena. Simulations are performed both at the device and chip level.
The following areas are where TCL currently focuses on:
Research Thrust 1:
Electro-Thermal Analysis and Reliability Study of Ultra Wide Bandgap (AlGaN, β-Ga2O3, Diamond) Power Electronics
Research Thrust 2:
Radiation Effects, Reliability, and Thermal Management of Lateral GaN High Electron Mobility Transistors and Micro-LED Arrays
Research Thrust 3:
Electro-Thermal Study of Wide Bandgap Vertical GaN Power Devices
Research Thrust 4:
Electro-Thermal Analysis of 2-D Layered Materials and Devices