JPH02230305A - Reference voltage source - Google Patents

Abstract

PURPOSE:To make an adjustment terminal for adjusting a reference voltage unnecessary by setting respectively different threshold voltages based on the difference of a work function between the gate electrode of a MOS transistor and a silicon substrate, and generating the difference of the threshold voltages to use as the reference voltages. CONSTITUTION:The MOS transistors 3 and 4 in a reference voltage device composed of MOS transistors 1-4 are set to be a pair whose threshold voltages are different, the difference of the threshold voltages is outputted to a point A, and the reference voltage is generated. For varying the threshold voltages of the MOS transistor 3 and the MOS transistor 4 for generating the reference voltage. The above mentioned source is provided with the MOS transistor 3 having the first gate of polysilicon to which the impurities of a first inductive type is introduced, and the MOS transistor 4 having the second gate electrode of polysilicon to which the impurities of the first inductive type and the impurities of a second inductive type whose density is comparatively high are introduced, and the same polarity as the MOS transistor 3. The difference of the threshold voltages is obtained by the difference of the work function between the material of the gate electrode and the silicon substrate. Thus, the adjustment terminal is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reference voltage source that can be built into a semiconductor integrated circuit (IC).

Conventionally, the reference voltage source within an IC has mainly been constructed from a Zener diode. In this case, there was a lot of variation in the Zener voltage, and the temperature characteristics were poor, so an adjustment terminal and compensation element were always required on the outside. Furthermore, Japanese Patent Laid-Open No. 53-47953 describes an embodiment in which the difference in threshold values due to channel dove is used as a reference voltage source, but this method is difficult to control the voltage due to variations in the dosing amount for the channel and the gate film thickness. The amount of variation in the power source is large, and it is difficult to obtain the desired voltage completely without adjustment, and some kind of adjustment function is required externally, which is extremely troublesome to use.

The object of the present invention is to eliminate such drawbacks,
The object of the present invention is to provide a method that minimizes variations due to the manufacturing process by using a constant work function difference depending on the material as a reference voltage.

FIG. 1 shows an embodiment in which the reference voltage source of the present invention is applied to a battery voltage detection circuit for an electronic watch. Transistor 1, 2
, 3.4 is the reference voltage source constructed by
Transistor 3 as detailed in No. 47953.
and transistor 4 are a pair with different threshold values, and the difference in threshold values is output to point A. Transistor 5 is switched by clock φ and performs sampling operation. Resistor 6 and resistor 7 are designed to divide the power supply voltage so that the potential at point B becomes the same as the potential at point A, which is the desired power supply voltage and the reference voltage output. Therefore, the output of the converter 11 becomes level "1" because the potential at point B is higher than the potential at point A at the initial power supply voltage. Also, as the power supply voltage decreases, the potential at point A becomes higher than point B, and the output of comparator l1 becomes level "0". The output of this comparator is stored in latch l2 using clock φ. In this example, the problem is how to create the threshold values of transistors 3 and 4, which serve as reference voltages. In the present invention, the difference in threshold value is obtained by the difference in work function between the material of the gate electrode and the silicon substrate. Normally, the threshold voltage vth of a transistor is determined by the following equation.

vth=φG−φ3+2φF +QD/CO+031/
Co 1 where φ. is the work function of the gate, φ3 is the work function of the substrate, φ′ is the Fermi level of the silicon surface, Q. is the amount of charge on the silicon surface, Qss is the interface state, C
0 represents the capacitance per unit area of the gate. This φ. is uniquely determined by the gate material. Also, φS on the silicon side. φ is also uniquely determined if the impurity distribution is constant.

As an example, in the case of a silicon gate structure, φ depends on the doping amount and type of the gate. can be determined arbitrarily. Second
The figure shows an N-channel transistor with a silicon gate structure. A P-well 25 is formed in an N-substrate 26, and 21 to 24 are diffusion layers that become sources and drains.
27 is Sin. 28 to 31 are A for electrodes.
It is l.

The gate electrode is 34.35 mm below which a conductive channel is formed via a gate oxide film. In a normal process, the gate electrode 34 of the transistor 32 is doped with N0, which is the same as the source and drain. On the other hand, transistor 33
The gate electrode 35 of is doped with P0. At this time, φG of the gate electrode 34 is +0.3 based on the intrinsic Fermi
〜＋〇． 5V, φ6 of the gate electrode 35 is -0.3 to -0. 5■. Therefore, φ3, 2φF, Qo/Co, Qss/C
Even if there is a large variation in o between processes, it is common to both transistors, so if we take the difference between the threshold values, we get:
0.6-1. depending on the gate doping amount. A reference voltage that changes by approximately Ov can be generated. Normally, the doping amount can be controlled fairly stably, and even if there is some variation, it is within ±10 mV. FIG. 3 shows an example of a structure in which the gate is diffused in the opposite type to the source and drain in a normal silicon gate process. P° diffusion layer 42.4 which becomes the source/drain on the N-substrate 41
3 is formed. At this time, P' also enters a part 46 of the gate electrode. After this, N is doped using the oxide film 44 as a mask. This is an example of a P-channel transistor, but N
Channels are also formed in the same way. Although the shikiness value is low under the gate electrode 45 and the shikishi value is low under the part 46, it can be considered that the shikishi value of the transistor is high.

FIG. 4 shows another example of the structure, (a). (C
) indicates the process order. (a) First, a gate oxide film 52 is applied to the base 53, and then polysilicon 51 is deposited. At this time, the polysilicon is heavily doped with N only in the necessary region 58. After that, the polysilicon is etched to form a gate 54. (C) After that, unnecessary parts of the gate film are removed to form 55, and the whole is P+
dove to form a sonis drain 56.57.

Since the gate 54 is set to N~ in advance, it does not change even if it is doped with P+.

As another method of the present invention, the work function difference between metal gates such as a /l gate and a Mo gate may be used, or the work function difference between a silicon gate and a metal gate may be used. The present invention is a method of creating a reference voltage using a stable gate work function, and since all factors under the gate that cause variations in the process are removed, a fairly stable reference voltage can be obtained. ．． For example, when the present invention is used as a reference voltage for a battery voltage detection circuit for an electronic watch, it does not require adjustment and can be easily built into the C. It has a large contribution to the development of technology, process reduction, and mass production.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a battery voltage detection circuit for an electronic watch using a reference voltage source according to the present invention. FIG. 2 is a diagram showing an example of the structure of a transistor bear with different threshold values for the present invention. FIG. 3 is a diagram showing an example of a high threshold value structure in a silicon gate transistor. Figure 4 is a diagram showing an example of the manufacturing process of a high threshold transistor. 3...High resistance value 4...Normal resistance value transistor 34...N+ 35...Gate doped with P0-V3S Figure 1 Applicant Seiko Epson Corporation Agent Patent attorney Kisaburo Suzuki et al. 1 person figure 2 procedural amendment (voluntary)

Claims (1)

[Claims] (1) A reference voltage source characterized by using the difference in threshold values of two transistors using gate materials whose gate electrodes have different work functions.