Single-Layer Polysilicon Reference Voltage Circuit

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Solution Overview

Problem

Existing reference voltage generation circuits in semiconductor devices face challenges due to manufacturing variations, leading to instability in the reference voltage, which requires complex configurations and increased layout area and adjustment steps.

Innovation Solution

A reference voltage generation circuit using nonvolatile storage elements formed by a single layer of polysilicon, where the elements can be adjusted into enhancement and depletion states to eliminate manufacturing variation effects, utilizing a series connection of depletion and enhancement type transistors to generate a precise reference voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional reference voltage generation circuits are used, then the circuit can generate a reference voltage, but manufacturing variations cause the reference voltage to vary significantly from the desired value

Engineering Contradiction:

Improvereference voltage precisionVSAvoidreference voltage stability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the physical state of the transistor by converting it from an enhancement type to a depletion type through charge injection into a floating gate. This parameter change allows the transistor to operate in the depletion mode, providing stable constant current characteristics that are insensitive to manufacturing variations in threshold voltage

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The depletion type transistor automatically provides constant current characteristics when its gate and source are connected, without requiring external control circuits or adjustment mechanisms. The transistor self-regulates the current flow based on its depletion mode operation, eliminating the need for complex auxiliary circuits

Inventive Principle:

Principle #25Self-service

2Manufacturing precision

If auxiliary transistors are added to correct reference voltage variation, then the reference voltage precision can be improved, but the layout area and number of adjustment steps increase

Engineering Contradiction:

Improvereference voltage precisionVSAvoidcircuit configuration complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent extracts the essential function of constant current generation from a complex auxiliary transistor network and implements it using a single depletion type transistor with gate-source connection. This extraction simplifies the circuit by removing unnecessary components while retaining the voltage correction capability

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of using enhancement type transistors with complex control mechanisms to achieve constant current, the patent inverts the approach by using depletion type transistors with gate-source connection, which naturally provide constant current characteristics without additional control circuits

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS10446567B2Nonvolatile storage element and reference voltage generation circuit

Publication Date: 2019.10.15 ASAHI KASEI MICRODEVICES CORP

AI summary

To provide a nonvolatile storage element capable of being formed by an ordinary CMOS process using single layer polysilicon without requiring exclusive forming process and a reference voltage generation circuit with high versatility and high precision. A reference voltage generation circuit includes nonvolatile storage elements formed of single layer polysilicon. The nonvolatile storage elements each include a MOS transistor including a floating gate, a MOS transistor including a floating gate, and a MOS transistor including a floating gate.