2-Inch Diamond Wafer Growth and High-Power Diamond MOSFET Fabrication—Nov. 29

Seminar presented by the Microsystems Technology Laboratories.

Tuesday, November 29, 2022
11:00 AM - 12:00 PM ET
MIT.nano, Building 12 Room 3005

Speaker: Professor Makoto Kasu, Department of Electrical and Electronic Engineering, Saga University, Japan
Host: Professor Jesús del Alamo, Donner Professor and Professor of Electrical Engineering in the Department of Electrical Engineering and Computer Science, MIT
T Diamond possesses a wider bandgap (5.47 eV), higher breakdown electric field (>10 MV/cm), higher thermal conductivity (22 W/cmK), and higher electron and hole mobilities (4500 and 3800 cm2/Vs, respectively) than GaN and SiC. Therefore, diamond is considered to be the most capable candidate for the power semiconductor device application [1].

Till now, diamond single-crystal substrates have been limited to sizes of 4 mm. Recently, diametrically inch-wide diamond wafers can be grown on Ir/sapphire (a-Al2O3) (110) substrate [2]. Microneedle technology was employed to delaminate the diamond layer from the substrate without cracking [2]. This is improved more recently [3] when a misoriented sapphire substrate is used to develop (and delaminate, without microneedles) a stable, two-inch-diameter diamond wafer. This wafer exhibits the highest crystal quality, with an XRC (004) FWHM of 98 arcsec.

We then fabricated diamond p-channel MOSFETs on heteroepitaxial diamond wafers [4]. We performed NO2 p-type doping on the H-terminated diamond and used an Al2O3 layer for gate insulation and surface passivation. The drain current–voltage (ID–VDS) characteristics of this MOSFET [4]. The maximum ID was 0.68 A/mm. A low ON resistance of 50 Ω∙mm was obtained. The low values of RC and RSH enabled the MOSFET to conduct high values of current and exhibit low resistance.

The off-state drain current characteristic of the MOSFET at VGS = 7 V indicates a high breakdown voltage (VBR) of −2568 V [4]. The specific on-state resistance, (RON,spec) was determined to be 7.54 mΩ∙cm2. Consequently, the BFOM (= VBR2/RON,spec ) — where VBR, LSD, and 2LT were −2568 V, 13.6 µm, and 1.48 µm, respectively — was determined to be 874.6 MW/cm2, the highest ever in diamond.

[1]    Makoto Kasu, Jpn. J. Appl. Phys. 56, 01AA01 (2017).
[2]    Seong-Woo Kim, Makoto Kasu et al., Appl. Phys. Lett. 117, 202102 (2020).
[3]    Seong-Woo Kim, Makoto Kasu et al., Appl. Phys. Express 14, 115501 (2021).
[4]    Niloy Chandra Saha, Makoto Kasu et al., IEEE Electron Device Letters 43, 777 (2022).

About Makoto Kasu
1990 PhD degree in electrical engineering, Kyoto University (Prof. Akio Sasaki)
1990-2011 NTT Laboratories
2002-2003 Visiting researcher at University Ulm (Prof. Erhard Kohn)
2011- Full professor in Saga University