R&D of diamond films in Kobe Steel

K. Kobashi and Y. Yokota

Frontier Carbon Technology Project/JFCC

Center for Advanced Research Projects (6F), Osaka University

2-1 Yamada-oka, Suita, Osaka 565-0871, Japan

N. Kawakami, T. Tachibana, K. Hayashi, and K. Inoue

Kobe Steel, Ltd., Electronics Research Laboratory

1-5-5 Takatsuka-dai, Nishi-ku, Kobe 651-2271, Japan

Abstract

Kobe Steel, Ltd. (KSL) started R&D of diamond films in 1985, aiming at electronic applications. Its R&D history is approximately divided into three stages: the first stage was from 1985 up to 1995, when basic technologies for device fabrication were developed. The second stage was after 1995 up to now, when the developed technologies are employed to make individual test devices such as gas sensors, ultraviolet (UV) sensors, and field effect transistors (FETs) for feasibility studies. The third stage began from 1998 with the Frontier Carbon Technology (FCT) Project of Japan Fine Ceramics Center (JFCC) and runs in parallel to the second stage. In this stage, both heteroepitaxial growth and large area deposition of diamond films are the main interest of KSL that has been studying scientifically the morphology and growth of diamond films since 1985.

In this paper, we present the current R&D status of diamond film technologies and applications in KSL. In particular, the latest results on three topics, gas sensors, UV sensors, and FETs, will be described in detail, which will be useful for this conference to consider the prospects for diamond film device applications in the near future.

(1) gas sensors

Conventionally, electrolyte-type systems are used for sensing semiconductor doping gases such as PH₃ and AsH₃. It is however expected that both the size and the maintenance cost would be greatly reduced if they can be replaced with solid-state sensors. In association with New Cosmos Electric Co., Ltd., we were able to fabricate diamond film gas sensors that have very high sensitivities (the change in electrical resistance was more than 20 %). The selectivity against alcohol and hydrogen was reasonably high.

(2) UV sensors

Diamond film is known to be a most appropriate material for UV detection with solar-blind characteristics. We fabricated UV sensors that have interdigited electrodes on highly oriented, undoped diamond films. Its temporal photoresponse was investigated by the group of Prof. A. Gicquel at LIMHP-CNRS, France. It was found that the fabricated diamond UV sensors detect and follow the incident UV laser pulse with a FWHM of 10 ns.

(3) FETs

A new type of FETs, called p⁺-i-p⁺ FETs, were fabricated using electron beam lithography combined with B-ion implantation to make gate and source-drain structures, respectively. It was found that the holes injected from the source travel through the undoped diamond channel under the gate to the drain by the space-charge-limited-current mechanism. The transconductance was 1 mS/mm. This device was able to circumvent fundamental problems associated with standard Metal-Semiconductor (MS)-FET devices of diamond existing so far.

This work was supported by FCT Project, which was consigned to JFCC by NEDO.

Koji Kobashi

FCT/JFCC

Center for Advanced Research Projects (6F), Osaka University

2-1 Yamada-oka, Suita, Osaka 565-0871, Japan

k-kobashi@rd.kcrl.kobelco.co.jp

Fax: +81-6-6879-4147, Phone: +81-6-6879-4146

Keywords: diamond, sensors, transistors