Semiconductor memory device

Abstract

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 voltageportion 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 anda 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; acomparator 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.

Description

technical field [0001] The present invention relates to a semiconductor memory device provided with an electrical measurement function capable of directly measuring the characteristics of nonvolatile memory cells such as EEPROM and ROM in which data can be written and erased by electrical manipulation from the outside. Background technique [0002] Conventionally, in evaluating the characteristics of memory cells in a nonvolatile semiconductor memory device such as an EEPROM, each memory cell in the semiconductor memory device is directly measured from the outside. [0003] For example, in the case of EEPROM, in the case of erasing data in the memory cell M, and in the case of writing data in the memory cell M, when evaluating electrical characteristics such as the threshold voltage Vth of the memory cell M in various states, such as Figure 10 (data erasure) or Figure 11 As shown in "Data Writing", it is set that the gate of the memory cell M can be changed arbitrarily fro...

AI Technical Summary

Problems solved by technology

[0017] However, when testing, V SS (V SS = 0, the voltage is below 0V), so when the threshold voltage Vth is a negative potential, it is impossible to use the same test method as the positive potential for the traditional circuit structure

Images