Tatsuya Kamei

Silicon p-n junction photodiodes sensitive to ultraviolet radiation

Experimental studies on a silicon photodiode have been carried out to achieve the performance characteristics required for applications such as spectroscopic measurements. Sheet resistance was applied as a control parameter for diffusion to obtain a shallow junction less than 1 µm in depth. For high ultraviolet responsivity, the diffusion layer, in which a built-in field is induced by the impurity gradient, was optimized for values of the sheet resistance of about 800-2000 Ω/□. The device responded in the wavelength range of 200-1000 nm,and had a responsivity of 0.065 A/W at 200 nm. In order to reduce influence of stray light in spectroscopic measurements, two types of photodiodes were fabricated with photoresponse reduced in the long-wavelength portion. A p+-n-p+device was found preferable to a p+-n-n+device. And the device structure with an extended electrode was desirable for high, reliable performance.

Practical size limits of high voltage IC's

To develop high voltage ICs of small chip sizes, relationships between geometrical parameters and electrical properties of dielectrically isolated high voltage devices were investigated, and practical size limits of the lateral devices were determined. Device techniques for electric field reduction and efficient carrier transfer were introduced. Using these techniques, each of the thyristor and an ac switch was fabricated in the area of 0.07 mm2and 2.03mm2per one crosspoint pairs. Their main specifications were 350 V blocking voltage, 250 mA dc current and 7 ω on-resistance.

Electrical Characteristics of Ultrahigh-Voltage Thyristors and Related Problems

Ultrahigh-voltage thyristors with a blocking voltage of 4-10 kV were developed by double diffusion technique. A new surface contouring technique realized in this development gives excellent blocking characteristics and is effective in minimizing the reduction of current-carrying area. To study the feasibility of ultrahigh-voltage thyristors, their electrical characteristics were estimated. According to the experimental results, the blocking voltage is restricted by their dynamic properties, especially turn-off time. The limit for the rated voltage may be about 5 kV at the present stage.

High voltage integrated circuits for telecommunications

First, the recent progress in high voltage integrated circuits in Japan will be reviewed. Next, a family of high voltage integrated circuits with a blocking voltage of 350 V will be presented. These ICs are composed of thyristor switching elements, high voltage drivers and control circuits. The device is integrated on a dielectrically isolated substrate using a high voltage bipolar technology. In order to prevent deformation of the substrate during high temperature processing, a newly developed multi-polysilicon layer technology is applied to make the substrate. Both theoretical and experimental work has been done to reduce the electric field at the junction termination. On-state characteristics of the lateral thyristor have also been studied. Results from these studies will be presented.

“Integrated Photo-coupled Semiconductor Crosspoint Switches”

Integrated photo-coupled crosspoint switches using thyristors are investigated. In comparison with current-coupled crosspoint switches, these offer the advantage of having little electric interference between switches and control circuits. In order to realize both easy mounting and low triggering gate power, an efficient photo-coupling using both an edge emitting LED and a lateral thyristor is developed, and an accurate alignment technique utilizing the surface tension of solder is also developed. A trade-off between triggering gate sensitivity and the allowable dv/dt capability is improved by a new photo-coupled PNPN switch circuit. The developed device has low triggering gate current (15?30 mA for 4 thyristors) and a high dv/dt capability (>1000 V/?s). A switch network fabricated by newly developed devices is seen to have good transmission characteristics.

A Light Activated High Power Bidirectional Thyristor

A new type of light activated bidirectional thyristor device is presented. It has an improved commutating dV/dt characteristic of 100 V/µs and has ratings of 1000 V for blocking voltage and 100 A for current capability. In this device, two thyristors and a GaAs light emitting diode are optically coupled so that both thyristors can be directly triggered by a light signal from the diode. This device has been developed taking into consideration the necessity of a trade-off between triggering sensitivity and an allowable voltage increasing rate, dV/dt, and with the use of a highly efficient optical coupling structure between the light emitting diode and the thyristors.

On Determination of Gold Trap Concentration in Diffused Silicon pn Junctions

On diffused silicon pn junctions doped with gold, junction capacitance for very low and high frequencies was analyzed and gold trap concentration was determined by measurement of junction capacitance on the basis of the analysis. It is concluded that the gold trap concentration gives reasonable value, because the gold trap concentration in the diffused diodes quenched after gold diffusion agrees with the gold concentration determined by the tracer analysis with Au198. The values of the gold trap concentration in the diffused diodes quenched after gold diffusion are almost equal to the solubility of the interstitial gold, but they are less for more slowly cooled diodes and the diodes alloyed after gold diffusion.

The Dielectrically Isolated High Voltage IC Technology

The dielectrically isolated high voltage IC technology was investigated. The diode structure with n+ buried layer as a channel stopper can achieve a high breakdown voltage for the same oxide thickness as compared with a conventional structure. The relations between diode parameters and the breakdown voltage were investigated and a control technique for the fixed charge density was applied to obtain the high voltage device. The dependence of the device characteristics on positions in the IC was studied and it was found that current gain of lateral pnp transisters depended on the positions significantly. The high voltage crossunder interconnection structure utilizing the n+ buried layer was developed. Using all these techniques, a 250 V analog IC and 350 V switching ICs for telecommunication were fabricated.