Ferroelectric AlN Gate Layer for Reversible Polarization in GaN Transistors
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Solution Overview
Problem
Conventional ferroelectric materials like AlGaN/GaN heterostructures lack reversible polarization, limiting their application in high-speed electronic devices and capacitors due to non-reversible spontaneous and piezoelectric polarizations.
Innovation Solution
A thin film of AlN or AlGaN is formed with ferroelectric properties by controlling thickness and applying tensile stress through lattice mismatch with the GaN layer, enabling reversible polarization and improved crystallinity using an argon plasma process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AlGaN/GaN heterostructure is used, then high electron sheet concentration and low sheet resistance are achieved, but reversible polarization is lost
Solution Approach 1:
The patent changes the crystal structure parameter of AlN from wurtzite to rock-salt phase through high-pressure synthesis conditions. This parameter change enables reversible polarization in the AlN layer, resolving the contradiction between maintaining high electron concentration and achieving reversible polarization for high-speed device operation.
Solution Approach 2:
The patent creates a composite heterostructure combining AlN (with induced rock-salt phase) and GaN layers. This composite material system combines the high electron sheet concentration properties of AlGaN/GaN with the reversible polarization capability of rock-salt AlN, enabling both high productivity and reliability.
2Reliability
If AlN or AlGaN is formed with conventional methods, then spontaneous and piezoelectric polarizations are achieved, but reversibility is limited
Solution Approach 1:
The patent utilizes a phase transition from wurtzite to rock-salt structure in AlN through high-pressure synthesis. This phase transition fundamentally changes the polarization characteristics from non-reversible (spontaneous and piezoelectric) to reversible (ferroelectric), enabling reliable ferroelectric properties and improving device switching capability.
3Speed
If thin film of AlN or AlGaN is formed to enhance ferroelectric properties, then charge carrier movement speed improves, but manufacturing complexity increases
Solution Approach 1:
The patent changes the synthesis parameter (applying high pressure) to induce rock-salt phase formation directly during film deposition. This approach enhances ferroelectric properties and charge carrier movement speed while avoiding the need for separate post-processing steps, thereby managing manufacturing complexity.
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
This approach enhances the ferroelectric properties of AlN or AlGaN, facilitating high-speed charge carrier movement, improved turn-off characteristics, and negative capacitance effects, suitable for high-speed transistors and memory cells.
Implementation Method 1
A ferroelectric material includes a spontaneous electric polarization that can be reversed by changing an electrical field applied to the ferroelectric material
Implementation Method 2
a thin film of AlN or AlGaN that exhibits ferroelectric properties is formed between a gate electrode and a second semiconductor layer
Data Source
AI summary
Techniques in accordance with embodiments described herein are directed to semiconductor devices including a layer of aluminum nitride AlN or aluminum gallium nitride AlGaN as a ferroelectric layer and a method of making a thin film of AlN/AlGaN that possesses ferroelectric properties. In a ferroelectric transistor, a thin film of AlN/AlGaN that exhibits ferroelectric properties is formed between a gate electrode and a second semiconductor layer, e.g., of GaN.