JP2910458B2 - Field effect transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an individual semiconductor device MOS.
Field-effect transistor, and more particularly, to a MOS field-effect transistor having a substantially low gate threshold voltage.

[0002]

2. Description of the Related Art In a conventional MOS type field effect transistor (hereinafter referred to as a MOSFET) as an individual semiconductor element,
An external terminal is connected to the gate electrode of the MOSFET itself to input a gate voltage to drive the MOSFET. This M
The driving capability of the OSFET depends on the gate threshold voltage of the MOSFET. In other words, if the gate threshold voltage is large, the driving capability of the MOSFET decreases,
Cannot fully utilize the performance of Therefore, it is necessary to realize a MOSFET having a low gate threshold voltage, and in order to reduce the gate threshold voltage, various measures such as process parameters in manufacturing the MOSFET have been devised. For example, a MOS transistor having a low gate threshold voltage can be driven by a manufacturing process such as reducing the thickness of the gate oxide film of the MOSFET or suppressing the substrate impurity concentration in the channel portion.
An FET is obtained.

[0003]

However, in a conventional MOSFET as a discrete semiconductor device, if the gate threshold voltage is lowered, a sufficient noise margin cannot be secured at high temperatures due to the negative temperature coefficient of the gate threshold voltage itself. Therefore, there is a problem that the operating temperature range is narrowly limited.

FIG. 2 (b) shows a currently obtained MOSFET.
An example of a temperature characteristic of the gate threshold voltage V _{GS (th)} of FIG. V
_{GS (th)} is 1.0 V at 25 ° C., and its temperature coefficient k is −
In order to secure a noise margin of 0.5 V at 5 mV / ° C., the maximum channel temperature Tchmax is set to 125 ° C.
The operating temperature range is limited below. Further, considering the manufacturing variation of V _{GS (th)} , the practical operating temperature range is 100 ° C.
Must be restricted to: This operating temperature does not satisfy the above-mentioned maximum channel temperature Tchmax specification of 150 ° C.

On the other hand, a MOSFET connecting a gate surge voltage protection circuit between a gate portion of the MOSFET and an external gate terminal does not have a function of actively changing the gate threshold voltage of the MOSFET, and has a MOSFET.
The drive capability of T could not be prevented from lowering.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a MOSFET having a driving capability with a substantially low threshold voltage.

[0007]

The field effect transistor of the present invention has a gate threshold voltage compensating circuit comprising a diode connected in series, which is forward-biased by the voltage of a Zener diode, and a resistor connected in parallel with the diode. A configuration is provided for connection between the terminal and an external gate terminal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 shows a first embodiment of a field effect transistor according to the present invention. FIG. 1 shows a basic configuration of this embodiment.
Referring to (d), MOSFET 1 is a MOSFET
1 between the gate 3 and the outer end gate terminal 2
Are arranged.

FIG. 1A shows a MOSF including a compensation circuit.
2 shows the configuration of ET. In other words, two series-biased forward-biased diodes 6 and a resistor R15 are connected between the gate 3 of the MOSFET 1 and the external gate terminal 2 by a Zener diode 8 externally biased via the sub-terminal 4. .

Next, the MOSFE according to the first embodiment of the present invention will be described.
The characteristic value of T will be described.

The gate threshold voltage inherent to the MOSFET is Th
= 25 ° C., V _{GS (th)} = 2.4 V, and its temperature coefficient is k
_{VG (th)} = − 5 mV / ° C., Zener diode 8 is MOS
The FET is made of polysilicon on an oxide film, and its zener voltage Vz is 3V.

The two series diodes 6 are MOSFETs
Composed of polysilicon on an oxide film having a reference voltage of 25 ° C.
In a 2 · V _F = 1.4V, its temperature coefficient 2 · k _VF =
−2 mV / ° C.

A resistor (R1) 5 connected between the gate 3 and the external gate terminal 2 is composed of a polysilicon resistor provided on an oxide film of a MOSFET, and has a resistance value of 1 to 10.
It is assumed to be 0Ω.

The resistor (R2) 7 is also made of a polysilicon resistor, but has a resistance value that satisfies the expression (1) in order to forward bias the diode 6 with the Zener voltage Vz. That is, R2 <R1 (Vz−2 · V _F ) / 2 · V _F (1) As described above, the provision of the compensation circuit 12 allows the gate threshold voltage V of the MOSFET to be shown in FIG.
The characteristics of the _{GS (th),} can be improved in temperature characteristics of the effective gate threshold voltage V _{GS (th)} eff shown in Figure 1 (c).

Next, referring to FIG. 3 showing a second embodiment of the present invention, the gate threshold voltage compensating circuit 3 of the MOSFET 1 will be described.
0 is caused by a Zener voltage of a Zener diode 38 biased by a series-connected photodiode 10 optically excited by optical coupling with four or more sets of LEDs 11 arranged in parallel between a gate external terminal 32 and a source terminal S. Forward-biased two-series diode 36 and resistor 3
5 is arranged between the gate external terminal 32 and the gate 33. Photodiode array 10 Zeder diode 38, diode 36 and resistors 35, 37 and 39 are formed of polysilicon on the oxide film of the MOSFET.

With the configuration of the second embodiment, the gate can be driven by a single gate signal source without using a sub terminal and a separate power supply.

[0018]

As described above, according to the present invention, the MOSF
By disposing a gate threshold voltage compensating circuit between the gate 2 of the ET1 and the external gate terminal 3, the effective gate threshold voltage V _{GS (th)} eff at Tch = 25 ° C. (Tch = 25 ° C.)
_{= V GS (th) -2 ·} V F = 2.4-1.4 = 1.0
(V), its temperature coefficient k _{VGS (th)} eff = k _{VGS (th)} −
A field effect transistor having the characteristic of 2 · kV _F = −5 − (− 4) = − 1 (mV / ° C.) is provided.

According to the present invention, in the case of the above characteristic example, the effective gate threshold voltage is V _{GS (th)} eff (Tch = 150 ° C. ₎ at Tch = 150 ° C.
° C) = 0.875 V, Tch = −55 ° C., and V _{GS (th)} eff (Tch = −55
° C) = 1.080 V, and the entire channel temperature of the MOSFET can be set to the effective operating temperature range.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a field effect transistor according to a first embodiment of the present invention; FIG. 1A is a diagram showing a configuration of the field effect transistor according to the first embodiment of the present invention; FIG. 3A is a graph showing a gate threshold voltage characteristic of a transistor and FIG. 4C is a graph showing a temperature characteristic of a diode forward voltage. FIG. 3C is a graph showing a temperature characteristic of an effective gate threshold voltage of the transistor shown in FIG. FIG. 2 is a diagram illustrating a basic configuration of a field-effect transistor according to one embodiment.

FIG. 2 is a view showing a conventional field effect transistor;
(A) is a configuration diagram, and (b) is a temperature characteristic diagram of a gate threshold voltage.

FIG. 3 is a diagram illustrating a configuration of a field effect transistor according to a second embodiment of the present invention.

[Explanation of symbols]

 1,31 MOSFET 3,33 Gate 2,32 External gate terminal 4 Sub terminal 5,7,35,37,39 Resistance 6 Diode 8 Zener diode 10 Photodiode array 11 LED 12,30 Compensation circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 29/78 H01L 27/088 H03K 17/687

Claims (1)

(57) [Claims] An electric field for connecting a gate threshold voltage compensating circuit comprising a diode connected in series and serially connected by a voltage of a Zener diode and a resistor connected in parallel to the diode between a gate terminal and an external gate terminal. Effect transistor.