JPH01220481A - Light-driven mosfet relay - Google Patents

Abstract

PURPOSE:To improve the light absorbing efficiency of photodiodes, by forming the gate electrode of a power MOSFET part with a high-melting.-point metal. CONSTITUTION:Light of a LED 5 hits Silicon on Insulator(SOI) photodiodes 4, and a power MOSFET is driven. Even if the light of the LED 5 is transmitted through the SOI photodiodes, the light is reflected by the high-melting-point metal of a gate electrode 2 of the power MOSFET. The reflected light is absorbed in the SOI photodiodes 4 again. Thus, the absorbing efficiency of the light in the SOI photodiodes 4 is improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is based on SOI (Silicon on In5u
The invention relates to an optically driven MO8FET relay with

This relay uses normal photodiode and power MOSF
Compared to a light-driven MO3FET relay that connects the ET with wire wiring and incorporates a light emitting diode into an l package, it is possible to reduce the size and cost by integrating the photodiode and power MO3FET into one chip. .

<Prior Art> FIG. 2 is a circuit diagram, and FIG. 3 is a schematic sectional view showing an example of a conventional structure. Usually, an insulating film 3 such as PSG is deposited and planarized on the gate electrode 2 made of polysilicon of the vertical power MOSFET 1, and then a polysilicon film is deposited. In this case, the thickness of the deposited polysilicon film is about 1 to 2 μm. A Sol photodiode 4 is formed from this polysilicon film. That is, the polysilicon film is sequentially melted and recrystallized using a laser, separated into appropriate sizes,
A PN junction of the photodiode is formed by a normal IC process. Wiring is performed simultaneously for the Sol photodiode 4 in the upper layer and the power MOSFET I in the lower layer.

In the above process, only laser remelting was described as a recrystallization method, but SO! There is no problem as long as the photodiode 4 is formed. The thus formed Sol photodiode 4 is assembled into one package and used so that light from a light emitting diode 5 made of GaAlAs, GaP or the like falls on it.

<Problems to be Solved by the Invention> In the above-mentioned Sol structure optically driven MOS relay, the film thickness of the photodiode 4 on the Sol is 1 to 2 μm due to crystallinity.
It can only be made very thin, about 300 ft thick. Therefore, there is a drawback that the light from the light emitting diode 5 cannot be completely absorbed, resulting in a low absorption efficiency.

Furthermore, research is currently underway to obtain a good film thickness for Sol, but the current situation is that it is currently difficult to dramatically increase the thickness due to crystallinity issues.

In view of the above, an object of the present invention is to provide a light-driven MOSFET relay with a simple configuration and high absorption efficiency.

<Means for Solving the Problems> The present invention provides that the gate electrode of the power MO8FET in the lower layer is
It is characterized by being made of a high melting point metal such as O, W or the like.

As a result of the above, the light from the light emitting diode that passes through the Sol photodiode without being fully absorbed is reflected by the high melting point metal of the gate electrode, and the reflected light is reabsorbed by the SOI photodiode. Efficiency can be greatly improved.

<Example> An example of the present invention will be described in detail with reference to FIG. Third
Parts having the same functions as those in the figures are designated by the same reference numerals. Note that the circuit configuration is the same as that in FIG. 2.

In FIG. 1, the gate electrode 2 is made of a high melting point metal such as MOIW instead of the conventional polysilicon. The other parts of the power MOSFETI are the same, 6 is the drain,
7 is an epitaxial layer, 8 is an n+ source region formed in the p-well, and 9 is a gate insulating layer. An insulating film 3 such as PSG is deposited on the gate electrode 2 made of a high melting point metal and after planarization, a polysilicon film is deposited to a thickness of about 1 to 2 μm.

After this polysilicon film is recrystallized using a laser, it is separated into appropriate sizes and photodiodes 4 are fabricated using the usual C process.

Incorporate light emitting diode 5! When assembled into a package, the light from the light emitting diode 5 hits the SO[photodiode 4 and drives the power MOSFET 1. Even if the light from the light emitting diode 5 is transmitted through the Sol photodiode 4, it is reflected by the gate electrode 2 and the reflected light is reabsorbed, so that the light absorption efficiency can be greatly improved.

<Effects of the Invention> As described above, according to the present invention, the lower power MO8FE
By using a high melting point metal for the gate electrode of T, So
The photodiode on the top of the photodiode can absorb even the reflected light from the gate electrode, increasing efficiency.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of main parts showing one embodiment of the present invention;
The figure is a circuit diagram, and FIG. 3 is a schematic sectional view of main parts showing a conventional example. 101. Power MO9FET, 2. ．． ．． Gate electrode, 4
1. , SOE photodiode, 511, light emitting diode. Agent Patent attorney Takeshi Sugiyama (1 other person) No. 7yA Figure 2 JJE diagram

Claims (1)

[Claims] 1. SOI (Silicon
A light-driven MOSFET relay with an onInsulstor structure, characterized in that the gate electrode of the power MOSFET part is formed of a high-melting point metal.
FET relay.