Shared-Drain Oxide TFT Access Cell Layout for Low-Temperature BEOL

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Solution Overview

Problem

Existing thin film transistors (TFTs) made of oxide semiconductors face challenges in BEOL integration without damaging previously fabricated FEOL devices due to high processing temperatures.

Innovation Solution

The formation of drain-sharing thin film access transistors using semiconducting metal oxide plates with shared drain electrodes and source electrodes, integrated with CMOS transistors, allows for low-temperature processing and efficient area utilization, while maintaining electrical connectivity through metal interconnect structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high processing temperatures are used to fabricate thin film transistors, then the transistor performance is improved, but previously fabricated FEOL devices are damaged

Engineering Contradiction:

Improvetransistor performanceVSAvoiddamage to FEOL devices

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the processing temperature parameter from high temperature to low temperature (below 400°C) to enable BEOL integration without damaging previously fabricated FEOL devices, while still achieving functional thin film transistors with oxide semiconductor channels

Inventive Principle:

Principle #35Parameter changes

2Reliability

If separate drain electrodes are used for each access transistor, then the electrical connectivity is optimized, but the area usage increases

Engineering Contradiction:

Improveelectrical connectivityVSAvoidmemory cell area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent merges the drain electrodes of two access transistors into a single shared drain electrode, reducing the area required for each memory cell while maintaining proper electrical connectivity through the shared structure

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The shared drain electrode serves multiple functions by acting as the drain for two different access transistors simultaneously, enabling more efficient area utilization in the memory cell structure

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12538475B2Drain sharing for memory cell thin film access transistors and methods for forming the same

Publication Date: 2026.01.27 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A first thin film transistor and a second thin film transistor include a semiconducting metal oxide plate located over a substrate, and a set of electrode structures located on the semiconducting metal oxide plate and comprising, from one side to another, a first source electrode, a first gate electrode, a drain electrode, a second gate electrode, and a second source electrode. A bit line is electrically connected to the drain electrode, and laterally extends along a horizontal direction. A first capacitor structure includes a first conductive node that is electrically connected to the first source electrode. A second capacitor structure includes a second conductive node that is electrically connected to the second source electrode.