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Japanese team releases diamond MOSFET to promote the popularization and practical application of diamond semiconductors
2024-01-12 10:45:58
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Waseda University and Power Diamonds Systems (PDS) developed a structure in which the diamond surface is covered with silicon oxide terminations (C-Si-O terminations) that turn off the transistor when the gate voltage is 0V. To this end they announced the development of a "normally off" diamond MOSFET.
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Waseda University and Power Diamonds Systems (PDS) developed a structure in which the diamond surface is covered with silicon oxide terminations (C-Si-O terminations) that turn off the transistor when the gate voltage is 0V. To this end they announced the development of a "normally off" diamond MOSFET.
The results were contributed by Professor Hiroshi Kawarada, FU Yu, Norito Narita, Xiahua Zhu, Waseda University Adjunct Professor Atsushi Hiraiwa, PDS's Kosuke Ota, PDS co-founder and CEO Tatsuya Fujishima and others. Details were announced on December 13 at IEEE International Electron Devices Meeting (IEDM 2023), an international conference on semiconductor device/process technology.
MOSFET
MOSFET is a field effect transistor (FET) with a MOS structure. It has the characteristics of high speed, low on-resistance, and high breakdown voltage. It is especially suitable as a switching element for motor driving. High-speed switching of large currents has been completed.
Therefore, if a normally-on device is applied to a power electronic device, there is no way to safely stop the device when it stops functioning normally, so normally-off operation is required. Against this background, the PDS and Waseda University research teams found that due to high-temperature oxidation, the C-H bonds of hydrogen atoms covering the diamond surface are transformed into CO bonds, and the surface becomes an electron defect, causing its performance to deteriorate. The company has been working on improving this to achieve stable operation of FETs.
In this study, we adopted a device structure in which the diamond surface has silicon oxide (C-Si-O) bonds instead of the traditional CO-Si bonds. As a result, the hole mobility of p-channel MOSFET is 150cm2/V·s, which is higher than the electron channel mobility of SiC n-channel MOSFET, and the signal threshold voltage of normally-off operation is 3~5V, which is the traditional diamond semiconductor Unachievable, a value said to prevent accidental conduction (short circuit).
In addition, the maximum drain current of PDS for horizontal silicon oxide terminated diamond MOSFET exceeds 300 mA/mm, and the maximum drain current of vertical silicon oxide terminated diamond MOSFET exceeds 200 mA/mm. This is said to be the highest value for a normally-off diamond MOSFET in the series.
Both companies claim that by covering their surfaces with C-Si-O bonds, they have become stable devices that are more resistant to high temperatures and oxidation than traditional CH surfaces, and the company believes that their usability makes them suitable for mass production. To this end, Professor Kawaharada believes that diamond power semiconductors that are easy to implement in society have been realized, and PDS will continue to strengthen the research and development of diamond MOSFETs in order to popularize and practicalize diamond semiconductors. Their goal is to develop a device process suitable for mass production and achieve higher voltage resistance with a simpler structure.
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