Bootstrapped TFT Logic Gates for Full-Swing Low-Leakage Circuits
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Solution Overview
Problem
Existing unipolar n-type Thin Film Transistors (TFTs) face challenges in realizing complex logic circuits due to low stage-to-stage gain and high static leakage-current, lacking the benefits of complementary transistor types.
Innovation Solution
The development of CMOS-like logic gates using unipolar n-type TFTs, which include a set of TFTs with pull-down, diode-connected, and output pull-up transistors, along with a capacitor to form a bootstrapped feedback network, reducing static leakage current and enabling full-output swing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional unipolar n-type TFTs are used to construct logic gates, then the device complexity is reduced and fabrication is simplified, but the static leakage current increases and stage-to-stage gain decreases
Solution Approach 1:
A capacitor is introduced as an intermediary component to store charge and maintain the bootstrapped feedback voltage, enabling the circuit to overcome the inherent limitations of unipolar TFTs without requiring complementary transistor types
Solution Approach 2:
A bootstrapped feedback network is implemented where the output voltage is fed back to the gate of the pull-down TFT through a capacitor, creating a positive feedback mechanism that amplifies the output swing and reduces leakage current by keeping the pull-down TFT in a more controlled state
2Device complexity
If conventional unipolar n-type TFTs are used to construct logic gates, then the device structure is simplified, but the stage-to-stage gain becomes insufficient for complex logic circuits
Solution Approach 1:
The bootstrapped feedback mechanism uses a capacitor to store and reuse the output voltage swing, providing additional voltage gain in each stage that enables reliable signal propagation through multiple logic stages without requiring complex complementary transistor structures
3Area of stationary object
If conventional inverter configuration with two TFTs is used, then the device footprint is minimized, but the output voltage swing is reduced and logic functionality is lost after a few stages
Solution Approach 1:
The bootstrapped feedback network captures the output voltage swing and feeds it back to enhance the gate voltage of the pull-down TFT, effectively amplifying the output swing beyond what a conventional two-TFT inverter can achieve and maintaining logic functionality across multiple stages
Solution Approach 2:
The capacitor acts as an intermediary energy storage element that preserves the voltage swing information and delivers it back to the circuit at the appropriate moment, enabling full-swing output without increasing the fundamental transistor count
Data Source
AI summary
The disclosure is directed at a CMOS-like logic gate including a set of thin-film transistors (TFTs), the set of TFTs including a subset of pull down TFTs, a subset of diode-connected TFTs and an output pull-up transistor; and a capacitor; wherein the subset of diode-connected TFTs, the output pull-up transistor and the capacitor are positioned to provide a bootstrapped feedback network to provide full-output swing; and wherein the subset of diode-connected TFTs and one of the subset of pull-down TFTs form a leakage current path; and wherein at least one of the subset of pull-down TFTs is connected to a first input.