Energy Efficient Devices and Electromechanics

The need for higher efficiency in eco-friendly vehicles has stimulated research on GaN based power devices. GaN devices suffer from less leakage current and has higher critical field, breakdown voltages and power density compared to Si or GaAs devices. Compared to 4H-SiC, GaN has its competitive edge in high bandwidth application with smaller, lighter package. Since power devices handle large amount of power, high temperature stability is critical. However, GaN suffers from lower thermal conductivity compared to 4H-SiC. We intend us utilize hexagonal Boron Nitride (h-BN) at the interface of GaN devices to enhance the heat transfer characteristics of the device. h-BN is a remarkable 2D thermal conductor with lateral heat transfer coefficient higher than that of copper. We expect the highly efficient heat transfer with the device will enhance the thermal stability of GaN based power electronics in eco-friendly vehicles. As a postdoctoral researcher at Stanford, I also analyzed and determined that 2D material surfaces devoid of dangling bonds are ideal contacts for nanomechanical switches with zero off-state leakage power. This is attributed to the low surface energy of the basal plane. 2D materials were found to be excellent interfacial materials for decreasing adhesive forces (capillary and van der Waals forces) during switching operations, which reduced pull-in and release voltages as well as power consumption.

Current applications of interest include:

Electromechanics of Eco-friendly Vehicles
Power devices based on GaN
Ultra low power devices and memory

Related Publications

Ahn, Chiyui, Scott W. Fong, Yongsung Kim, Seunghyun Lee, Aditya Sood, Christopher M. Neumann, Mehdi Asheghi, Kenneth E. Goodson, Eric Pop, and H-S. Philip Wong. ‘‘Energy-efficient phase-change memory with graphene as a thermal barrier", Nano Letters 15, no. 10 (2015): 6809-6814.

Seunghyun Lee, Alvin Tang, James P. McVittie, H. -S. Philip Wong, ‘‘NEM relays using 2-dimensional nanomaterials for low energy contacts", Energy Efficient Electronic Systems, pp. 1,2.

Seunghyun Lee, Joon Sohn, Zizhen Jiang, Hong-Yu Chen, and H. -S. Philip Wong, ‘‘Metal Oxide Resistive Memory using Graphene Edge Electrode", Nature Communications 6, 8407.

Seunghyun Lee, Kyunghoon Lee, Chang-Hua Liu, Girish S. Kulkarni, and Zhaohui Zhong, ‘‘Flexible and Transparent All-Graphene Circuits for Quaternary Digital Modulations", Nature Communications, 3, 1018 (2012).

Seunghyun Lee, Seow Yuen Yee, Ali Besharatian, Hanseup Kim, and Khalil Najafi, ‘‘Adaptive gas pumping by controlled timing of active microvalves in peristaltic micropumps", in IEEE Solid-State Sensors, Actuators and Microsystems, Denver, Colorado.

Hanseup Kim, Seunghyun Lee, Khalil Najafi, “High force liquid gap electrostatic hydraulic micro actuator”, The 11th International Conference on Miniaturized Systems for Chemistry and Life Sciences (μTAS), pp. 1735-1737