JPH0247866B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor integrated circuit, and particularly to a semiconductor integrated circuit using a plurality of nonvolatile memory elements using floating gates. The present invention also devises an element that is easy to use in a PLA type circuit.

An object of the present invention is to provide an element that can be easily applied to highly integrated circuits such as PLA type circuits with almost no increase in area, and to provide an integrated circuit using the same, a PLA type circuit, etc. This is what I am trying to do. Conventionally, these elements and circuit configurations have been formed by fusing wiring materials, transistors with floating gates called FAMOS, and the like. The fusing type and the diode destruction type have disadvantages in that they cannot be rewritten and require a large current. Furthermore, FAMOS type devices are not suitable for high integration because they require transistors to be configured. The present invention was devised to eliminate the above drawbacks.

A memory element forming part of the present invention is shown in FIG.

In Figure 1, 1 is an N-type substrate, 2 is an N-type diffusion layer, and 3 is an N-type substrate.
4 is a P-type diffusion layer, 4 is an oxide film, 5 is a floating gate made of a polycrystalline silicon film, and 6 is a wiring.

The operation of this device utilizes the fact that the depletion layer near the diffusion layer 3 changes depending on whether or not charges are accumulated in the floating gate, and the junction breakdown voltage rises and falls. Injection into the floating gate is achieved by a portion of the junction breakdown current reaching the floating gate with high energy. The amount of injection at this time depends on the voltage, and the current also needs to be above a certain level.

FIG. 2 shows the depletion layer 7 before implantation, and FIG. 3 shows the depletion layer 8 after implantation. Since the junction breakdown voltage is inversely proportional to the width of this depletion layer, it corresponds to the characteristics 9 and 10 in FIG. 4, respectively. The states shown in FIGS. 2 and 3 are provided for each element, respectively, and the voltage is used as Va when operating the circuit. At the time of Va, current flows when the characteristic is 9, and it does not flow when the characteristic is 10. This allows it to function as a memory element. Furthermore, when the voltage is around Va, the reverse breakdown current is small, and no charge is injected into the floating gate. Furthermore, when there is a difference in breakdown voltage due to device variations, the diffusion concentration and substrate concentration may be set so that the highest breakdown voltage among the variations is lower than Va. At this time, devices with a low breakdown voltage have a large breakdown current, so charge is injected into the floating gate, and all the elements are at a voltage slightly lower than Va.
Breakdown voltage is unified. Therefore, in the device of the present invention, there is almost no need to consider variations between devices.
In addition, rewriting of this element is done using a floating gate MOS
Like (FAMOS), it can be easily erased with ultraviolet light.
Furthermore, since this device is formed from only a junction and a floating gate, the area can be kept as small as possible.

PLA type circuits are composed of a combination of AND and OR, and the actually required circuit is determined by selecting which wirings to perform AND and OR between. Therefore, an element that uses conduction and non-conduction in junctions, such as the present element, is most suitable for such a PLA type circuit, and can provide a highly integrated and rewritable integrated circuit without increasing area. Further, such an element can be expected to have a wide range of applications, not limited to this.

As described above, the present invention is highly integrated, rewritable,
It has a simple structure and is easy to use.
The present invention provides a nonvolatile memory element that can eliminate variations between elements, and a semiconductor integrated circuit that integrates a plurality of nonvolatile memory elements.

[Brief explanation of drawings]

Fig. 1... A cross-sectional view of the semiconductor memory element which is the basis of the present invention, Figs. 2 and 3... A diagram of changes in the depletion layer of the element shown in Fig. 1, Fig. 4... A diagram of electrical characteristics of the element shown in Fig. 1. .

Claims (1)

[Claims] 1. In a PLA (Programmable Logic Array) type integrated circuit, a diode is installed on a semiconductor substrate, a dielectric film is placed on the junction of the diode, and a multilayer circuit is placed through the dielectric film. A semiconductor integrated circuit characterized by comprising a floating gate made of a crystalline silicon film.