Semiconductor Memory Comparator Test Circuit
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Solution Overview
Problem
Conventional semiconductor memory devices face inefficiencies in evaluating memory cell characteristics when the threshold voltage is negative, requiring longer test times and higher manufacturing costs due to the inability to apply negative voltages externally, which limits the use of existing test methods.
Innovation Solution
A semiconductor memory device that adjusts the reference current or voltage to change the decision level of a comparator, allowing for the same test method to be used for both positive and negative threshold voltages, eliminating the need for external switches and simplifying the circuit structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external ammeter measurement method is used for negative threshold voltage, then measurement can be performed, but test time becomes approximately ten times longer
Solution Approach 1:
The invention changes the measurement parameter from external current measurement to internal voltage comparison. By converting the measurement method to use a comparator that compares drain voltage with a reference voltage, the test time is reduced from approximately ten times longer to the same duration as positive threshold voltage testing.
2Adaptability or versatility
If negative voltage is applied from external terminal to gate, then same test method as positive potential can be used, but conventional circuit structure cannot support it due to parasitic diodes
Solution Approach 1:
Instead of applying negative voltage to the gate as in conventional methods, the invention inverts the approach by applying positive voltage and using a comparator to detect when the drain voltage exceeds the reference voltage. This eliminates the need for negative voltage application while achieving the same measurement objective.
Solution Approach 2:
The invention introduces a comparator as an intermediary device between the memory cell and the measurement system. The comparator mediates the measurement process by comparing the drain voltage with a reference voltage, eliminating the need for direct negative voltage application to the gate and avoiding the parasitic diode limitation.
3Measurement precision
If different test methods are used for positive and negative threshold voltage, then measurement can be performed, but device complexity increases with multiple switches and circuits
Solution Approach 1:
The invention creates a universal test method that works for both positive and negative threshold voltages using the same circuit configuration. The comparator-based measurement approach serves multiple functions: it can evaluate both positive and negative threshold voltages, eliminate the need for additional switches, and provide a unified measurement procedure for all memory cells regardless of threshold voltage polarity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces test time and manufacturing costs by enabling efficient evaluation of memory cell characteristics regardless of threshold voltage polarity, while simplifying the circuit design.
Implementation Method 1
a comparator for detecting whether or not a drain voltage that is a voltage of the drain has exceeded the reference voltage
Data Source
AI summary
Provided is a semiconductor memory device, which realizes characteristic evaluation even in a case where a threshold voltage is a negative potential by a test method which is similar to a case of a positive potential. The semiconductor memory device includes a plurality of memory cells for storing data. When a test signal is input, the semiconductor memory device changes from a normal mode to a test mode for evaluating characteristics of the plurality of memory cells. The semiconductor memory device also includes: a memory cell selecting portion for selecting a memory cell; a constant voltage portion for generating a reference voltage; a constant current portion for generating a reference current; an X switch voltage switching control circuit for supplying one of an X selection signal and a voltage signal input from an external terminal to a gate of the memory cell; a Y switch portion for supplying the reference current to a drain of the memory cell selected by a Y selection signal; a comparator for detecting whether or not a drain voltage that is a voltage of the drain has exceeded the reference voltage; and a decision level changing portion for adjusting a current value of the reference current and a voltage value of the reference voltage so as to change a decision level of the comparator based on a control signal in the test mode.