Gallium Nitride-Based Integrated Circuits

Student: Rohith Allaparthi

Degree: M.S., Summer 2021

Major Professor: Dr. Morgan E. Ware

Research Area(s):

Microelectronics

Conventional Materials & Processes

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Background/Relevance

  • Gallium nitride (GaN) is a semiconductor material with high band gap and high electron mobility, and is great for high frequencies, high temperature, and high-power applications. However, GaN devices are limited by n-type doping, reproducibility, and high dislocation density problems currently.

 

Innovation

  • Fabrication of capacitors using AlN as the dielectric material which has an operating range up to 600 °C.

  • Fabrication of a GaN-based Integrated circuits using the monolithic growth of AlN capacitors and HEMTs.

Approach

  • Monolithic growth of GaN, AlGaN, and AlN layers using MBE system and defining structures by etching and metal deposition.
    • A simple charge pump circuit, DC-DC voltage converter, consisting of four AlGaN/GaN HEMTs and an AlN capacitor, as shown in fig. b, is chosen for the initial tests.
    • AlN-based capacitor is shown in fig. a.

Key Results

  • Successful demonstration of operation at 310 °C with almost no loss in capacitance while a commercial one failed over 250 °C (fig. c and fig. d). Tested for scalability of capacitance with increased area.
  • Photomasks designed for the IC processing is shown in fig. e.

Conclusions

  • A novel AlN capacitor is fabricated, characterized, and integrated into modules. A monolithic growth of GaN-based IC is demonstrated to have good surface morphology and crystallinity. This will avoid the necessity of cooling devices and optimizes power density.

  • Fabricated capacitor is also tested with system level design circuits and displayed wide temperature operation.

Future Work

  • Scaling up the capacitance and improving the operating voltage range. Test for higher temperatures up to 600 °C.

  • Fabricating a complex integrated circuits.