Shared-Gate Transistor Unit for Sub-Word Line Speed and Oxide Protection
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Solution Overview
Problem
Semiconductor memory devices face speed delays due to increased memory cells connected to word lines, leading to inefficiencies in voltage distribution, and existing methods for addressing these delays are inadequate in managing defective drains and preventing gate oxide layer bursting.
Innovation Solution
The implementation of transistor units with a shared gate structure, featuring an active area divided by a separation area and a gate with an inverted pi () shape, which separates channels effectively and prevents gate oxide layer bursting, while allowing for efficient management of defective drains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If one word line is divided into multiple sub-word lines to reduce speed delay, then voltage distribution speed is improved, but device complexity increases due to multiple sub-word line drivers
Solution Approach 1:
The patent merges two separate transistor structures into a single integrated transistor unit with a shared gate. The active area contains a body with a protrusion, where separation areas divide the body into two portions and the protrusion into two parts, forming two transistors that share common gate and source structures. This integration reduces the number of independent driver circuits needed while maintaining the sub-word line functionality for improved voltage distribution speed.
2Productivity
If channel length is reduced to increase transistor density, then productivity is improved, but short channel effects increase reducing reliability
Solution Approach 1:
The patent introduces a vertical protrusion structure extending from the body in the second direction, creating a three-dimensional active area configuration. This dimensional change allows the channel to extend both horizontally in the body and vertically through the protrusion, effectively increasing the channel length without proportionally increasing the planar footprint. The separation areas strategically positioned within the body and protrusion enable this extended channel geometry, maintaining transistor density while reducing short channel effects through the longer effective channel length.
3Reliability
If gate structure covers entire active area to improve transistor control, then reliability is improved, but gate oxide layer bursting occurs due to field concentration at corners
Solution Approach 1:
The patent segments the gate structure into multiple parts that selectively cover different regions of the active area. The gate is divided into a first gate portion covering the body and a second gate portion covering the protrusion, with channel avoidance regions positioned at the corners of the body where the gate does not extend. This segmentation allows the gate to control the channel effectively in covered regions while avoiding field concentration at the corner regions, preventing gate oxide layer bursting.
Solution Approach 2:
The separation areas act as intermediary regions between the gate structure and the corner portions of the active area. These separation areas are positioned between the gate and the corners, serving as buffer zones that prevent direct field concentration at the corner regions. The separation areas extend in the second direction through the body and into the protrusion, creating a physical and electrical intermediary that protects the gate oxide layer from bursting while maintaining proper channel control in the active regions.
Data Source
AI summary
A transistor with a shared gate structure includes an active area and a gate. The active area has a body extending in a first direction on a substrate, and a protrusion extending in a second direction perpendicular to the first direction from a central portion of the body in the first direction. The gate is arranged above the active area to overlap a channel area of the active area, and has an inverted pi () structure that, from a plan view, surrounds on three sides but does not cover a portion of the active area that includes two corner portions of the active area. The active area is divided into a first active area and a second active area by a separation area extending in the second direction and separating the body and a portion of the protrusion. The protrusion is divided into a first portion separated into two sub-portions by the separation area and a second portion, wherein the first portion is between the body and the second portion in the second direction. Opposite ends of the body in the first direction corresponding to two drain areas, the second portion of the protrusion corresponding to a common source area, and the gate constitute two transistors, wherein the two transistors share the gate.