QAFE Gate Stack Composition for Low-Hysteresis NC-FET Switching
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Solution Overview
Problem
The challenge in developing negative-capacitance field-effect transistors (NC-FETs) is to achieve steep subthreshold swing (SS) below 60 mV/decade while minimizing hysteresis and reducing the onset voltage, which is essential for low-power consumption and scalable transistor design, but current solutions face issues with asymmetric SS and high off-state leakage current.
Innovation Solution
The use of a quasi-antiferroelectric (QAFE) material in the gate stack of NC-FETs, which introduces negative capacitance without hysteresis, achieved by forming a QAFE layer of Hf1-xZrxO2 with a zirconium atomic percentage between 50% and 75%, allowing for operation at sub-60 mV/decade SS with reduced onset voltage and negligible hysteresis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a ferroelectric material is used in the gate stack to achieve negative capacitance, then subthreshold swing below 60 mV/decade is achieved, but hysteresis and high off-state leakage current occur
Solution Approach 1:
The patent changes the composition parameter of the gate stack by incorporating a specific ratio of HfO2 and ZrO2 (where Zr content is 20-80 atomic percent) to achieve QAFE properties. This compositional parameter change enables negative capacitance with reduced hysteresis and lower off-state leakage compared to conventional ferroelectric materials
Solution Approach 2:
The patent uses a composite material system combining HfO2 and ZrO2 in specific proportions to create a quasi-antiferroelectric gate dielectric. This composite approach leverages the complementary properties of both materials to achieve negative capacitance effect while minimizing the harmful effects of hysteresis and leakage current
2Device complexity
If conventional MOSFET structure is used, then device simplicity is maintained, but subthreshold swing cannot go below 60 mV/decade
Solution Approach 1:
The patent modifies the electrical parameter of the gate dielectric by using QAFE material with specific compositional ratios (Hf1-xZrxO2 where x=0.20-0.80), which enables negative capacitance effect and achieves subthreshold swing below 60 mV/decade while maintaining a relatively simple FET structure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The QAFE material enables NC-FETs to operate at steep subthreshold swing with no hysteresis, reducing gate leakage current and achieving bi-directional SS below 60 mV/decade, thereby addressing the limitations of existing NC-FETs and improving power efficiency and scalability.
Implementation Method 1
a quasi-antiferroelectric (QAFE) material in the gate stack of NC-FETs, which introduces negative capacitance without hysteresis
Implementation Method 2
forming a QAFE layer of Hf1-xZrxO2 with a zirconium atomic percentage between 50% and 75%
Data Source
AI summary
A method includes forming an interfacial layer over a substrate; forming a quasi-antiferroelectric (QAFE) layer over the interfacial layer, in which forming the QAFE layer comprises performing an atomic layer deposition (ALD) cycle, and the ALD cycle includes performing a first sub-cycle for X time(s), in which the first sub-cycle comprises providing a Zr-containing precursor; performing a second sub-cycle for Y time(s), in which the second sub-cycle comprises providing a Hf-containing precursor; and performing a third sub-cycle for Z time(s), in which the third sub-cycle comprises providing a Zr-containing precursor, and in which X+Z is at least three times Y; and forming a gate electrode over the QAFE layer.