Science and Technology of Integrated Super-High Dielectric Constant AlO x /TiO y Nanolaminates / Diamond for MOS Capacitors and MOSFETs Jiangwei Liu a, * , Orlando Auciello b, c , Elida de Obaldia b, d , Bo Da e , Yasuo Koide a a Research Center for Functional Materials, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki, 305-0044, Japan b Department of Materials Science and Engineering, University of Texas at Dallas, 800W Campbell Rd, Richardson, TX, 75080, USA c Department of Bioengineering, University of Texas at Dallas, 800W Campbell Rd, Richardson, TX, 75080, USA d Facultad de Ciencia y Tecnología, Universidad Tecnol ogica de Panam a, CVía Centenario. Anc on Panama, Panama e Research and Services Division of Materials Data and Integrated System, NIMS, Namiki 1-1, Tsukuba, Ibaraki, 305-0044, Japan article info Article history: Received 4 September 2020 Received in revised form 5 October 2020 Accepted 7 October 2020 Available online 9 October 2020 Keywords: Diamond MOSFET Super-high dielectric constant AlOx/TiOy nanolaminate abstract A super-high dielectric constant AlO x /TiO y nanolaminate film is grown on hydrogenated diamond (H- diamond) to enable superior metal-oxide-semiconductor (MOS) capacitors and MOS field-effect tran- sistors (MOSFETs). In order to minimize or suppress leakage current, a nanometer thick AlO x film is inserted at the AlO x /TiO y nanolaminate/H-diamond interface. The maximum values for the capacitance density and dielectric constant related to the summation of individual AlO x and nanolaminate are 1.06 mF/cm 2 and 68.7, respectively. Capacitance density and dielectric constant for the AlO x /TiO y nano- laminate are as high as 5.22 mF/cm 2 and 308, respectively. Electrical properties of four H-diamond MOSFETs with gate lengths increasing from 2.4 mm to 10.1 mm were investigated. All of them showed p- type behavior and distinct pinch-off characteristics with drain current maxima of 47.4, 43.3, 26.6, and 24.6 mA/mm, respectively. On/off ratios and threshold voltages for the MOSFETs are higher than 10 4 and lower than 0.55 ± 0.10 V, respectively. The low threshold voltages indicate that the AlO x /TiO y nanolaminate gate-based MOSFETs can switch between ON and OFF stages at low gate voltages. Effective mobilities of the H-diamond channel layers for all the MOSFETs raised firstly and dropped subsequently with increasing voltages, which can be explained by the effect of mobility limiting factors. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Diamond has been studied extensively for use in high-power, high-frequency, and high-temperature device applications because of its wide band gap (~5.5 eV), high breakdown field (5e10 MV/cm), high carrier mobility (>3000 cm 2 /V$s), and high thermal conductivity (~2100 W/K$m) [1e3]. However, develop- ment of diamond electronic devices is limited by its quite low free carrier density caused by the high activation energies of boron (370 meV) and phosphorus (570 meV) dopants [4]. Fortunately, hydrogenated diamond (H-diamond) can accumulate two- dimensional hole gases on its surface with sheet hole densities of ~10 14 /cm 2 [5]. Therefore, the H-diamond is believed to be a promising channel layer for fabrication of high-performance dia- mond electronic devices. Recently, the H-diamond-based metal- oxide-semiconductor field-effect transistors (MOSFETs) have attracted great interest [6e9]. Breakdown voltage and operation temperature of these MOSFETs reached 2000 V and 400  C, respectively [6,7]. Radiofrequency power density and cut-off fre- quency of the investigated MOSFETs increased to 3.8 W/mm and 70 GHz, respectively [8,9]. Output current of the H-diamond MOSFETs is an important parameter to promote them for the high-power and high- frequency applications. Up to now, drain current maximum (I D,max ) of the H-diamond MOSFETs with an Al 2 O 3 as the gate dielectric was 1350 mA/mm [10]. This high output current benefited from NO 2 treatment for the H-diamond surface to enhance channel’s hole density [5], the polycrystalline H-diamond channel with hole density of the (110) or (111) plane higher than that of the (100) plane [11], and a submicrometric gate length (L G ) for the MOSFET. The output current of the MOSFET is also directly proportional to capacitance density of the gate oxide [12]. In order to further improve the I D,max for the H-diamond MOSFET, it is essential to develop new gate oxides with high capacitance * Corresponding author. E-mail address: Liu.jiangwei@nims.go.jp (J. Liu). Contents lists available at ScienceDirect Carbon journal homepage: www.elsevier.com/locate/carbon https://doi.org/10.1016/j.carbon.2020.10.031 0008-6223/© 2020 Elsevier Ltd. All rights reserved. Carbon 172 (2021) 112e121