Mis-transistor-based nonvolatile memory circuit with stable and enhanced performance

Abstract

A memory circuit includes a latch having a first node and a second node, a MIS transistor having a gate node, a first source / drain node coupled to the first node of the latch, and a second source / drain node, and a control circuit configured to control the gate node and second source / drain node to make a lingering change in a threshold voltage of the MIS transistor in a first operation and to cause the latch in a second operation to store data responsive to whether a lingering change in the threshold voltage is present, wherein the MIS transistor includes diffusion regions, a gate electrode, and sidewalls, wherein a metallurgical junction of each of the diffusion regions is positioned under the gate electrode, and a lateral boundary of a depletion layer in the diffusion region serving as a drain is positioned under a corresponding one of the sidewalls in the first operation.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The disclosures herein generally relate to a memory circuit, and particularly relate to a nonvolatile memory circuit which is capable of retaining stored data in the absence of a power supply voltage.[0003]2. Description of the Related Art[0004]Conventionally, a nonvolatile memory cell requires a special structure such as a floating gate or a special material such as a ferroelectric material or ferromagnetic material for the purpose of achieving nonvolatile data retention. There is a new type of nonvolatile semiconductor memory device called PermSRAM, which uses a MIS (metal-insulating film-semiconductor) transistor as a nonvolatile memory cell (i.e. the basic unit of data storage). The MIS transistor used as a nonvolatile memory cell in PermSRAM has the same structure as ordinary MIS transistors used for conventional transistor functions (e.g., switching function), and do not require a special structure or a special ma...

AI Technical Summary

Benefits of technology

[0010]It is a general object of the present invention to provide a memory circuit that substantially eliminates one or more problems caused by the limitations and disadvantages of the related art.

[0013]According to at least one embodiment of the present invention, a metallurgical junction of each of the diffusion regions is positioned under the gate electrode. Such a configuration ensures that the threshold voltage of the transistor is rather stable against manufacturing variation. Further, a lateral boundary of a depletion layer in one of the diffusion regions serving as a drain is positioned under a corresponding one of the sidewalls in the first operation. With this configuration, hot carriers generated by impact ionization at the drain / channel boundary are easily injected into the sidewall, thereby achieving a large, sustainable change in the transistor characteristics.

Problems solved by technology

That is, carriers trapped in the sidewalls tend to stay trapped longer than carriers trapped in the insulating film.

Images