Ryoichi Ishihara

Effects of Light Pulse Duration on Excimer-Laser Crystallization Characteristics of Silicon Thin Films.

The waveform of an excimer-laser light pulse has been varied using two laser systems with a delayed trigger. The effects of the pulse duration on the physical properties of crystallized silicon thin films were studied. From the results that threshold energies for crystallization, amorphization and ablation increased in proportion to the square root of light pulse duration, their critical temperatures were estimated to be 1000°C, 1800°C and 2700°C, respectively. It was found that the critical temperature for µ-crystallzation is changed from about 2600°C for a thin film under short pulse duration conditions to 1800°C for a thick film under long pulse duration conditions. The long pulse is effective, but not drastic, in improving the poly-crystallized silicon film quality.

Advanced excimer-laser crystallization process for single-crystalline thin film transistors

Abstract This paper reviews advanced excimer-laser crystallization techniques, developed by our group, enabling precise location-control of the individual Si grains. Combined microstructure and time-resolved optical reflectivity investigations during conventional excimer-laser crystallization showed that explosive crystallization occurs during excimer-laser irradiation. The location-control methods use local structural modification in the underlying materials (substrate) using a conventional photolithography. With the developed process, the large grains having a diameter of 6 μm can be set precisely at predetermined positions. We will also discuss the performance of the single-crystalline Si TFTs that are formed within the location-controlled Si grains. The field-effect mobility for electrons is 430 cm2/Vxa0s on average, which is well comparable to that of TFTs made with silicon-on-insulator wafers.

Single-Grain Si TFTs Fabricated From Sputtered Si on a Polyimide Substrate

Single-grain (SG) Si TFTs were fabricated from sputtered a-Si to achieve high performance TFTs on a polyimide substrate using a low temperature (350 °C) process including μ-Czochralski crystallization. The carrier mobility is 309 cm²/V·s and 126 cm²/V·s for electrons and holes, respectively. The devices are also successfully transferred to a flexible polyethylene naphyhalate (PEN) foil.

A Flexible Ultrathin-Body Single-Photon Avalanche Diode With Dual-Side Illumination

The worlds first flexible ultrathin-body dual-side illumination single-photon avalanche diode (SPAD) is reported with a peak photon detection probability of 11% in frontside-illumination (FSI) and 6% in backside-illumination modes, a dark count rate of 20 kHz and negligible afterpulsing and crosstalk. Compared with mainstream CMOS FSI SPAD, this device can be bent around a 10-mm-diameter cylinder and it is indicated in biomedical monitoring, implantable, and edible applications, as well as in antivignetting image sensors, bioinspired composite-eye, or flexible multiaperture cameras, and wherever the sensor plane must follow a certain curvature.

Location- and Orientation-Controlled (100) and (110) Single-Grain Si TFTs Without Seed Substrate

This paper reports on high-performance (100)- and (110)-oriented single-grain thin-film transistors (SG-TFTs) fabricated below 600°C without any seed substrate. Orientation has been controlled by μ-Czochralski process with an excimer laser. The field-effect mobility of the n-channel transistor is 998 cm²/V·s for (100) SG-TFTs and 811 cm²/V·s for (110) SG-TFTs. The field-effect mobility of the p-channel transistor is 292 cm²/V ·s for (100) SG-TFTs and 429 cm²/V ·s for (110) SG-TFTs.