JPH02197162A - Resistor - Google Patents

Abstract

PURPOSE:To enable a diffusion resistor to vary in resistance by stages in accordance with the increase of an applied voltage by a method wherein a diffusion layer is formed in such a constitution that two different spaces are combined to be provided in the diffusion layer. CONSTITUTION:A P<+>-type diffusion layer 40 are formed in meanders on an N-type Si substrate 44, which is covered with an SiO2 47, and electrodes 41 and 42 are provided, which are covered with an SiO2 48. When a p-n junction is reversely biased, a depletion layer is made to expand toward the substrate 44 side at a low voltage. When an Al film 49 is provided onto the P<+> layer 40 to serve as an optical shielding layer and connected to the electrode 41 of a low voltage, a depletion can be made to spread at a low voltage. When a reverse bias exceeds a specified value, depletion layers are linked together in the substrate 44 and a current flows direct without meandering, so that the diffusion layer 40 decreases in resistance. If the depletion layers are not linked together, the layer 40 is high in resistance. In the diffusion layer 40, when the combination of two different spaces in the layer 40 is changed, the layer 40 of optional resistance change characteristic can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a resistor formed on a semiconductor substrate, and is suitable as a resistor formed on a monolithic IC, for example.

[Prior Art] Conventionally, the resistance value of a resistor has been of a fixed type, a semi-fixed type, and one that changes continuously depending on an applied voltage. Fixed resistors include solid resistors and diffused resistors in semiconductor integrated circuits, while semi-fixed resistors include variable resistors with a mechanical slider that can be adjusted continuously depending on the applied voltage. An example of something that changes is the barista.

[Problems to be Solved by the Invention] By the way, if there were a resistor whose resistance value changed stepwise depending on the applied voltage, it would be possible to discriminate the level of an input signal with a simple configuration, which would be advantageous. Conceivable.

The present invention has been made in view of these points, and an object of the present invention is to provide a resistor whose resistance value changes stepwise depending on the applied voltage.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a second method for solving the problems.
As shown in the figure and FIG. 3, a diffusion region 40 in which impurities of different conductivity types are diffused into a semiconductor substrate 44 with a low impurity concentration.
The potential of the semiconductor substrate 44 is set so that the PN junction formed between the semiconductor substrate 44 and the diffusion region 40 is reverse biased, and the depletion layer formed between the diffusion region 40 and the semiconductor substrate 44 is expanded. In a resistor in which four aluminum films to which a potential is applied are arranged to cover a diffusion region 40, the diffusion region 40 is formed in a meandering manner at at least two different intervals, as shown in FIG. The two types of intervals are characterized in that they are set at such intervals that the depletion layer formed between the diffusion region 40 and the semiconductor substrate 44 gradually connects as the applied voltage increases.

Note that it goes without saying that the aluminum film 49 may be another metal film.

[Function] In the present invention, in the diffused resistor formed on the semiconductor substrate 44, two types of spacing between the diffused regions 40 are combined, so that the distance between the diffused regions 40 is The resistance value of the diffused resistor can be changed stepwise as the applied voltage increases.

[Example] FIG. 1 is a plan view showing a diffusion pattern of a resistor according to an example of the present invention. First, the operation of the resistor formed in the portion surrounded by the broken line C in FIG. 1 will be explained using FIGS. 2 to 5.

The resistors shown in Figures 2 and 3 (Patent Application No. 63-3248
(see No. 6) consists of a diffusion region 40 in which impurities of different conductivity types are diffused into a semiconductor substrate 44 with a low impurity concentration. Here, a semiconductor substrate 44 is formed by doping a single crystal silicon substrate on which a resistor is formed with N-type impurities at a low concentration. Furthermore, a diffusion region 40 in which P-type impurities are diffused at a high concentration is formed on the surface. As shown in FIG. 2, this diffusion region 40 is formed in a meandering manner.

Since the diffusion region 40 has a high impurity concentration, it is a low resistance layer, and the impurity! It has a resistivity corresponding to t#1 degree.

The surfaces of the diffusion region 40 and the impurity semiconductor substrate 44 are made of Si.
It is covered with an insulation 147 made of O2. Diffusion area 40
There are aluminum electrodes 41.4 in ohmic contact at both ends of the
2 are connected.

The resistance value between the aluminum electrodes 41 and 42 is the same as that of the diffusion region 4.
It is approximately determined by the resistivity of 0 and the width and length of the diffusion region 40.

The impurity concentration of the diffusion region 40 is highest at the surface, and the current density is higher near the surface.Therefore, the depth of the diffusion region 40 has little relation to the resistance value.In the embodiment, the ratio of the N-type impurity semiconductor substrate 44 The resistance is 60 Ωcab, the width of the P-type impurity diffusion region 40 is 3 μm, the pitch is 4 μm, B (boron) is used as the impurity, and the concentration is 2.5 × 10 ”
I set it to a dose.

One aluminum electrode 42 is also in ohmic contact with an impurity semiconductor substrate 44 in which N-type impurities are diffused at a low concentration. Therefore, the N-type impurity semiconductor substrate 44 is maintained at a stable potential.

Note that an electrode region 43 in which an N-type impurity is diffused at a high concentration is formed in a portion where the aluminum pole 42 and the impurity semiconductor substrate 44 make ohmic contact. After forming aluminum electrodes 41, 42 on the substrate, about 5,000 bassivations made of SiO2 are applied using the CVD method. 48 is attached.

When a voltage is applied to this resistor, the PN junction between the diffusion region 40 and the impurity semiconductor substrate 44 becomes reverse biased. Since the impurity concentration of the impurity semiconductor substrate 44 is low, even if the applied voltage is low, the depletion layer greatly expands toward the impurity semiconductor substrate 44 as shown by the broken line in FIG. 4(a). Furthermore, by connecting the light-shielding aluminum film 49 that exists on the diffusion region 40 to the low voltage side electrode [41], the field plate effect is strengthened and the depletion layer is expanded in a state where the applied voltage is low. becomes possible. Then, when the reverse bias voltage exceeds a predetermined value, FIG.
), the depletion layers in the impurity semiconductor substrate 44 are connected, and electrons can flow as shown by the arrows in the figure. Therefore, current flows through the meandering diffusion region 40 without meandering, and the resistance value of the resistor decreases. Also, when the input voltage is low, the fourth
As shown in the figure (,), since the depletion layers do not reach a connected state, a high resistance can be obtained by the meandering diffusion region 40.

FIG. 5 shows the relationship between the applied voltage and the current flowing through this resistor. In the figure, the relationship between the applied voltage and the conducting current when photovoltaic force is generated is as shown in the first quadrant,
When an applied voltage of more than a predetermined value (approximately 3V here) is applied,
The carrying current increases rapidly.

In the resistor shown in Figure 1, the resistance value between terminals A and B is approximately 4.9 MΩ when the applied voltage is low, but as the applied voltage increases, bunch through occurs in the area surrounded by broken line C. When this occurs, the resistance value between terminals A and B will be approximately 0.4MΩ, and if the applied voltage is further increased, damage will occur.
Bunch-through also occurs in the area surrounded by LD, and terminal A
, B is approximately 0.1 MΩ. The spacing of the diffusion patterns and the impurity concentration are set so that the bunch through in the area surrounded by the broken line C occurs at approximately 3 cm, and the bunch through in the area surrounded by the broken line C occurs at approximately 6 cm. ing.

A simple voltage discrimination circuit using the resistor RAB shown in FIG. 1 is shown in FIG. This circuit divides the input voltage Vin by the resistor RAB and the fixed resistor Ro, and outputs the voltage V.
This is to obtain out. Fixed resistor R.

The resistance value was 100 KΩ. In the same circuit, the change in the output voltage Vout when the input voltage Vin is changed in the range of 1 to IOV and the change in the resistance value of the resistor RA are shown in Figure 7. In Figure 7, the solid line indicates the output voltage VouL. , and the broken line indicates the resistance value of the resistor RAs.

Note that although the resistor of the present invention is particularly suitable for use in forming on a monolithic IC, it goes without saying that it can also be used as a single resistor.

[Effects of the Invention] In the resistor of the present invention, diffusion regions of different conductivity types are formed at least two types of intervals in a semiconductor substrate with a low impurity concentration, and the PN formed between the semiconductor substrate and the diffusion region is It can be easily manufactured using normal semiconductor manufacturing processes, which involves setting the potential of the semiconductor substrate so that the junction is reverse biased, and placing a metal film set at a potential that expands the depletion layer to cover the diffusion region. Despite the structure, it is possible to obtain a diffused resistance whose resistance value changes stepwise as the applied voltage increases. Furthermore, there is an advantage that an arbitrary resistance change characteristic can be realized by changing the combination of two types of intervals in the diffusion region.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a diffusion pattern of a resistor according to an embodiment of the present invention, FIGS. 2 and 3 are a perspective view and a sectional view respectively illustrating the configuration of the main parts of the same, and FIG. 4 is an explanatory diagram of the same operation as above, FIG. 5 is a diagram showing the voltage-current characteristics of the same as above, FIG. 6 is a circuit diagram showing an example of application of the above embodiment, and
The figure is an explanatory diagram of the same operation as above. 40 is a diffusion region, 44 is an impurity semiconductor substrate, and 49 is an aluminum film. FIG. 1 40...Diffusion region 44--Impurity semiconductor substrate

Claims (1)

[Claims] (1) A diffusion region in which impurities of different conductivity types are diffused is formed in a semiconductor substrate with a low impurity concentration, and the potential of the semiconductor substrate is set so that the PN junction generated between the semiconductor substrate and the diffusion region is reverse biased. , in a resistor in which a metal thin film to which a potential is applied to expand a depletion layer generated between the diffusion region and the semiconductor substrate is arranged so as to cover the diffusion region, the diffusion region is meandered at at least two different intervals. 2. A resistor, characterized in that the two types of intervals are set at intervals such that a depletion layer generated between the diffusion region and the semiconductor substrate gradually connects as the applied voltage increases.