Teruhito Ohnishi

Low-frequency noise characteristics in SiGe channel heterostructure dynamic threshold pMOSFET (HDTMOS)

We present the first investigation of low frequency noise in the SiGe channel heterostructure dynamic threshold p-MOSFET (HDTMOS). The sub-threshold characteristics and drain current noise were measured and evaluated. The input referred noise of the SiGe HDTMOS was reduced to about one-tenth compared with that of the Si MOS, because of higher transconductance g/sub m/ and less interface states at the Si/SiGe hetero-interface.

Low-Energy Double-Ion -Beam Deposition System

A low-energy double-ion-beam deposition system for high-quality thin-dielectric-film formation has been developed. The system consists of two beam lines (a mental ion beam line and a gas ion beam line) and has a new type of ion-beam deceleration electrodes which can be moved like a folding screen. In this system, decelerated Ta+ and oxygen ion beams of about 80 and 180 µA/cm2, respectively, were obtained in a final-energy range of 100~200 eV. In a deposition test, by simultaneously irradiating with a mass-separated Ta+ ion beam and an oxygen ion beam, pure and soichiometric Ta2O5 films of 50 nm thickness were obtained in one hour at room temperature.

Characteristics of Penning ionization gauge type compact microwave metal ion source

A sputtering ion source utilizing both microwave and Penning ionization gauge (PIG) ionizations for the primary ion beam deposition is described. The size of the source is 60 mm in diameter and 80 mm long. The continuous ion beams of refractory metals (Ta, W, Mo) with the ion currents of 100 to 150  μA are obtained for gas pressure on the order of 10−3 Torr in the plasma production chamber, microwave power under 40 W, and PIG discharge power under 80 W. This source has been operated with two different discharge modes, either glow discharge or arc discharge. Operation of both modes becomes quite stable by introducing microwave power. Metal ion production by glow discharge is more efficient in power consumption than that by arc discharge.

Sputtering ion source with simultaneous use of microwave and Penning‐ionization‐gauge discharge

Characteristics of Penning‐ionization‐gauge‐type compact microwave metal‐ion source are described. This ion source can operate with two different discharge modes: the positive‐resistance region mode and the negative‐resistance region mode. In the positive‐resistance region, a normalized emittance of a Ta+‐ion beam is 1.8×10−7 m rad, the plasma density is 4×1012 cm−3, and the electron temperature is about 6 eV. In the negative‐resistance region, the emittance is 2.7×10−7 m rad. This ion source is suitable for operation in the positive‐resistance region where the microwave discharge is dominant.

Ta2O5 film formation by double ion beam method

Abstract Ta2O5 thin films (20–40 nm thick) were formed on silicon substrates by double ion beam deposition method at room temperature. The films were annealed in a range of 400–600 °C for 15 min in N2 ambient. I–V and C−V properties of Ta2O5 fil were measured employing Al/Ta2O5/Si metal-insulator-semiconductor (MIS) capacitors. The smallest conductivity was found for Ta2O5 films annealed at 500°C and was as small as that for the 10 nm thick thermal SiO2 film. The dielectric constant of Ta2O5 films was about 13 as derived from the high frequency C–V measurements at 100 kHz. However, the Ta2O5 films formed by double ion beam deposition method have a large amount of positive fixed charges and/or oxide trap charges. Therefore, the flat band voltage of MIS capacitors becomes a large negative value. We confirm that these charges are made by irradiation of high energy electrons and high neutral atoms during the film deposition.

Base Current Control in Low-VBE-Operated SiGeC Heterojunction Bipolar Transistors Using SiGe-Cap Structure and High-Carbon-Content Base

We have demonstrated the low-VBE operation of SiGeC heterojunction bipolar transistors by introducing a novel device design concept using the SiGe cap structure and high Ge- (up to 25%) and C- (up to 0.8%) content base. We successfully controlled the base current by designing the SiGe cap structure and C content, which enabled us to obtain suitable values of hFE and BVCEO, while maintaining a high collector current and high-frequency performance. We clarified that the recombination around the emitter-base junction is enhanced by introducing the SiGe cap structure and high C content, which contribute to the increase of the base current.

Low-energy double ion-beam deposition of compound films

Abstract An ion-beam deposition system has been developed for the synthesis of refractory-metal compound films. The system has two beam lines for a metal and a gas ion. It is possible to decrease the ion energies to deposition energies in the range from a few tens to a few hundred electron volts, and to make the two-way (43°) ion beams overlap on the substrate. By simultaneously irradiating with a mass-separated refractory-metal (Ta, W or Mo) ion beam and a reactive-gas (oxygen or nitrogen) ion beam of 60–200 eV, TaO x , WO x , MoO x or TaN x films on a Si substrate were obtained at room temperature. Moreover, purity and stoichiometry of the deposited film depend on the deposition energy.