SRAM Transistor Mismatch Detection via Voltage-Current Curves

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Solution Overview

Problem

Current methods for detecting transistor mismatch in SRAM cells are time-consuming and costly, making them inconvenient for mass data collection and reducing product yield due to decreasing minimum supply voltage.

Innovation Solution

A method involving the use of measuring transistors and terminals to detect voltage-current curves of pull-up and pull-down transistors in SRAM cells, allowing for quick identification of mismatches by comparing these curves to determine transistor mismatch.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional positioning and measuring devices (Nano-prober/AFP) are used to detect transistor mismatch, then measurement precision is improved, but productivity deteriorates due to time-consuming and costly detection process

Engineering Contradiction:

Improvetransistor mismatch detection accuracyVSAvoiddetection speed and mass data collection efficiency

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent creates a copy of the transistor characteristics by generating voltage-current curves that represent the electrical behavior of pull-up and pull-down transistors. Instead of directly measuring physical transistor parameters with complex equipment, the method captures electrical characteristic curves that can be easily compared to identify mismatches, enabling fast and accurate detection without sophisticated positioning devices

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent changes the measurement parameters from direct physical transistor measurements to voltage-current characteristic curve measurements. By applying different voltages and measuring resulting currents to generate characteristic curves, the method transforms the detection problem into a parameter-based comparison that can be performed rapidly and accurately using simple measurement circuits

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If minimum supply voltage is decreased to improve SRAM performance, then power consumption is reduced, but manufacturing precision deteriorates due to increased transistor mismatch frequency

Engineering Contradiction:

Improvepower consumptionVSAvoidtransistor matching uniformity

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The patent enables the SRAM cell to self-diagnose transistor mismatches by incorporating measurement circuits that can detect voltage-current curve differences within the cell structure itself. This self-service capability allows manufacturers to identify and filter out mismatched cells during production, ensuring that only cells with proper transistor matching are used, thereby maintaining manufacturing precision even at lower supply voltages

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS9058902B2Method of detecting transistors mismatch in a SRAM cell

Publication Date: 2015.06.16 SHANGHAI HUALI MICROELECTRONICS CORP

AI summary

The present invention provides a method of detecting the transistor mismatch in a SRAM cell. The SRAM cell comprises two pass-gate transistors and a bi-stable circuit including two pull up transistors and two pull down transistors. The method comprises: providing two measuring transistors, whose gates are connected to a second word line, sources are connected to the outputs of the bi-stable circuit respectively and drains are connected to two measuring terminals respectively; turning on the measuring transistors and turning off the pass-gate transistors; detecting the voltage-current curve of the two pull down transistors and the two pull up transistors through the measuring transistors at the measuring terminals so as to detect the transistor mismatch in the SRAM cell.