JPH02122315A - Semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the production manhour and then the production cost by making the threshold voltage different with decreasing the thickness of the gate oxide film of one of paired MOSFETs of a reference voltage source compared with that of the other gate oxide film and supplying the difference of thickness between both oxide films as the reference voltage. CONSTITUTION:The gate G of a MOSFET 1 is connected to the source S of the FET 1 and to the inverted input of an operational amplifier 3. While the gate G of a MOSFET 2 is connected to the output of the amplifier 3. Both MOSFET 1 and 2 are obtained at one time in the manufacturing processes of an FET having a thin gate oxide film which forms a low breakdown strength logic part and an FET having a thick gate oxide film which forms a high breakdown strength output part respectively. Therefore, the thickness of the gate oxide film of the FET 1 is smaller than that of the FET 2. The difference VTH of the threshold voltage levels between both FET 1 and 2 due to the differ ence of film thickness is fed back via the amplifier 3. Thus the constant voltage is outputted. As a result, no ion implantation process is required when one of both MOSFETs is formed and therefore the production manhour is reduced for a semiconductor device together with the simplification of its structure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device having a built-in reference voltage source for obtaining a reference voltage necessary for a built-in element.

[Conventional technology]

In recent years, semiconductor devices have been developed in which a high-voltage output section and a low-voltage logic section coexist on-chip.

Even in such a semiconductor device, a reference voltage source that obtains a constant voltage with low fluctuations due to power supply voltage, temperature, etc. may be provided on-chip. Conventionally, this type of reference voltage source
As shown in the figure, a reference voltage is created with a MOSFET 5.6 connected between the external power supply voltage van and the ground via a resistor 4, and this is input to the operational amplifier 3, whose amplified output is output from one MOSFET 5. This is applied to the gate G.

One of the MOSFETs 5 and 6 for generating the reference voltage has a channel region having different conductivity by selective ion implantation, and the reference voltage can be obtained from the difference in dynamic resistance.

[Problem to be solved by the invention]

However, in the conventional reference voltage source of the semiconductor device described above, a selective ion implantation step is required to obtain one MOSFET 6, which increases the number of steps and increases the manufacturing cost.

The present invention solves the above problems, and its purpose is to eliminate the need for a special process for a pair of MOSFETs to obtain a reference power source in a device that has a high withstand voltage section and a low withstand voltage section on the same chip. The object of the present invention is to provide a semiconductor device with a high level of performance.

[Means to solve the problem]

In order to achieve the above object, the configuration of a semiconductor device according to the present invention includes a pair of MOSFETs that generate a difference between different threshold voltages as a reference voltage, and a gate oxide film of the pair of MOSFETs. are said to have different film thicknesses.

[Effect]

According to this configuration, of the pair of MOSFETs, the one with the thicker film thickness can be manufactured in the manufacturing process of the high voltage withstanding part, and the one with the thinner film thickness can be manufactured in the manufacturing process of the lower voltage part, so that the standard can be met. No special process is required for the pair of MOSFETs for power supply.

〔Example〕

Next, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a circuit diagram showing a reference voltage source in a first embodiment of a semiconductor device according to the present invention. Note that the same parts in FIG. 1 as those shown in FIG. 3 are given the same reference numerals.

1 is an enhancement type N-channel MO3FET connected between the Vooi source and ground via a resistor 4, and 2 is similarly V! 11 is an enhancement type N-channel MO3FET connected between a power supply and ground via a resistor 4. The gate G of MO3FETI is connected to its source S and to the inverting input of operational amplifier 3, and the gate G of MOSFET2 is connected to the output of operational amplifier 3. M.O.
SFET1 is made at the same time as the FET manufacturing process with a thin gate oxide film that constitutes the low voltage logic section, and is a MOSFET.
2 is an FET with a thick gate oxide film that constitutes a high breakdown voltage output section.
are made at the same time during the manufacturing process. Therefore, one MO3F
The thickness of the gate oxide film of the ETI is formed thinner than that of the other MOSFET 2. The threshold voltage difference ΔVT11 due to this difference in film thickness is given by the following equation.

ot O2 s s εS εO: Gate capacitance of MO3FET1: Gate capacitance of MO3FET2: Interface charge: Si (silicon) relative dielectric constant: Dielectric constant; Unit charge N5ub: Substrate concentration φf: Fermi potential This difference ΔVTH is applied to operational amplifier 3 By applying feedback, a constant voltage of Vo+ΔVT11 can be obtained, where Vo is the source voltage of MO3FETI.

FIG. 2 is a circuit diagram showing a second embodiment, in which the same parts as those shown in FIG. 1 are given the same reference numerals.

This embodiment differs from the first embodiment in that a depletion type N-channel MO3FETI' is used instead of the enhancement type N-channel MOSFET1, and this depletion type MO3FETI' is used in the process of the low breakdown voltage logic section. Since the thickness of the gate oxide film is thinner than that of the enhancement type N-channel MOSFET 2, the thickness of the gate oxide film is thinner than that of the enhancement type N-channel MOSFET 1'.
The gate G and drain D of are connected. In this configuration, the threshold voltage difference ΔVt* is output from the operational amplifier 3.

In this way, since the difference in threshold voltage due to the difference in gate oxide film thickness of both MO3FETI (1') and 2 is used as the reference voltage, one of the MOSFETs as in the conventional
There is no need to add an ion implantation process when forming the low-voltage logic section and the high-voltage output section, so the number of man-hours can be reduced and simplified, resulting in a low-cost semiconductor device. be done.

〔Effect of the invention〕

As explained above, in the semiconductor device according to the present invention, the gate oxide film thickness of one of a pair of MOSFETs serving as a reference voltage source is made thinner than that of the other to obtain different threshold voltages, and the difference is converted into a reference voltage. Since it is characterized in that it is supplied as a
Since a single ion implantation step in forming the ET is not required, the number of manufacturing steps can be reduced and the manufacturing cost can be reduced compared to the conventional method.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a reference voltage source in a first embodiment of a semiconductor device according to the present invention. FIG. 2 is a circuit diagram showing a reference voltage source in a second embodiment of the semiconductor device according to the present invention. FIG. 3 is a circuit diagram showing a reference voltage source in a conventional semiconductor device. l K) Acid ([4 thin enhancement type N
Channel MO5FET, 1' Depletion type N-channel MO3FET with thin gate oxide film 12 Enhancement type N-channel MO3F with thick gate oxide film
ET, 3 Operational Amplifier, 4 Fig. Section

Claims (1)

[Claims] (1) A semiconductor device incorporating a pair of MOSFETs that generate a difference between different threshold voltages as a reference voltage, the semiconductor device characterized in that the gate oxide films of the pair of MOSFETs have different thicknesses. Device.