Tsugio Kumai

Monolithic four-channel photodiode/amplifier receiver array integrated on a GaAs substrate

A four-channel optoelectronic integrated receiver array operating at the wavelength near 850 nm has been fabricated on a single GaAs substrate by using metal-semiconductor-metal (MSM) photodiodes (PDs) and metal-semiconductor field-effect transistors (MESFETs). The largest integration scale for a monolithic receiver and uniform characteristics among circuit channels have been achieved due to the structural simplicity and the process-compatibility of this array. Also, an extremely small capacitance of MSM-PD, 0.10 pF, has lead us to obtain a high-speed operation up to a bit rate of 1.5 Gbit/s, NRZ, and a low noise characteristic exhibiting an equivalent input noise current as small as 5 pA/Hz1/2. These results have indicated the suitability of MSM-PD/MESFETs circuits for large-scale multichannel optoelectronic integration of receivers.

High-performance, high-reliability InP/GaInAS p-i-n photodiodes and flip-chip integrated receivers for lightwave communications

High-performance, high-reliability InP/GaInAs p-i-n photodiodes have been developed for flip-chip integration. The introduction of ultra-small, planar junctions and microlenses has lead to a high quantum efficiency of 80%, a high-speed response of 21 GHz and a wide fiber alignment tolerance of over 40 mu m. The metallization structure based on an Au-Su/Pt system has been developed and its stability has been confirmed by photodiode aging at 180 degrees C for more than 3000 h. Applicability of flip-chip p-i-n photodiodes has been demonstrated by the fabrication of p-i-n/GaAs amplifier receivers. The minimization of parasitic reactances using flip-chip integration has resulted in a sensitivity of -27.4 dBm at 2 Gb/s, nonreturn-to-zero. These results show the usefulness of flip-chip integration for developing high-performance receivers for lightwave communication systems. >

GaAs optoelectronic integrated receiver with high-output fast-response characteristics

For obtaining high-output level and high-speed response in a GaAs-based optoelectronic integrated receiver, a circuit involving a two-stage amplifier was first designed and fabricated. A high sensitivity of 400 V/W has been achieved while preserving a high-speed response of 2-Gbit/s nonreturn to zero (NRZ).

High‐speed monolithically integrated GaAs photoreceiver using a metal‐semiconductor‐metal photodiode

A planar monolithically integrated GaAs photoreceiver involving a transimpedance preamplifier has been fabricated using a metal‐semiconductor‐metal (MSM) photodiode. The present MSM photodiode showed a small capacitance of 0.14 pF, which is much smaller than in conventional p‐i‐n photodiodes, and a high‐speed pulse response exhibiting a rise time of 300 ps was demonstrated. It is shown that an MSM photodiode is suitable for monolithic integration due not only to the simple process but also because of its high‐speed operation.

Preferential reaction and stability of the Au‐Sn/Pt system: Metallization structure for flip‐chip integration

Thermal reaction of a metallization system consisting of Au‐Sn solder, Pt/Ti barrier, and Au/Zn/Au contact layers formed on an InP substrate has been studied using Auger electron spectroscopy, scanning electron microscopy, and x‐ray diffractometry. Upon heating to 400 °C, no degradation of the Au/Zn/Au contact was noticed and moderate reaction was observed between Au‐Sn and Pt. The reaction shows a characteristic feature of preferential Pt‐Sn interdiffusion to produce an intermediate layer involving the PtSn phase. The effective diffusion coefficient exhibits an activation energy of 1.35 eV. The lifetime of this Pt barrier has been determined to be in excess of 108 h for 50 °C, being sufficient for the application of this metallization structure in practical device and flip‐chip integrated circuit fabrication.

High-speed flip-chip InP/InGaAs avalanche photodiodes with ultralow capacitance and large gain-bandwidth products

Planar InP/InGaAs avalanche photodiodes (APDs) have been fabricated by adopting a flip-chart configuration and a monolithic lens structure. These APDs exhibit an ultralow capacitance of 70 fF, a quantum efficiency of 80%, a wide bandwidth of 7 GHz, and a large gain-bandwidth product of 80 GHz.<<ETX>>

Thermal Stability of Au-Sn/Near Noble Metal Barrier Metallization Systems

We studied the reaction barrier characteriatics and thermal stability of evaporated Pd, Pt and Rh films when used with Au-Sn (30 wt% Sn). Sn in Au-Sn diffused preferentially into a barrier metal uniformly for all three metals. The diffusion coefficient was sufficiently small for Pt and Rh. Rh showed the samllest diffusion coefficient between 200°C and 400°C with the highest activation energy, 1.95 eV, below the melting point of Au-Sn (280°C). This result demonstrates the usefulness of Pt, and especially Rh, in highly stable metallization systems applicable to flip-chip integration.