AlScN Ferroelectric Layer Stack for Gate Control and Crystal Quality
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Solution Overview
Problem
Current ferroelectric field effect transistors (FE-FETs) face challenges in achieving efficient gate control and crystal quality due to limitations in the piezoelectric properties of materials used, particularly in maintaining the wurtzite structure while enhancing the piezoelectric effect.
Innovation Solution
The development of aluminum scandium nitride (AlScN) alloys, where scandium is introduced into aluminum nitride (AlN) to increase piezoelectric effects, is used to form a ferroelectric material sandwiched between the gate electrode and source-drain conduction region, with specific deposition processes to create layers with varying scandium content gradients for improved crystal quality and strain relaxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If aluminum nitride (AlN) is used as the ferroelectric material, then the wurtzite crystal structure is maintained, but the piezoelectric effect is insufficient for efficient gate control
Solution Approach 1:
The patent uses aluminum scandium nitride (AlScN) composite material, combining aluminum nitride (AlN) and scandium nitride (ScN) in a wurtzite crystal structure. The scandium content is controlled at 1-20% to enhance the piezoelectric effect while preserving the structural stability of AlN, thereby resolving the contradiction between maintaining wurtzite structure and improving piezoelectric properties
Solution Approach 2:
The patent modifies the compositional parameter by introducing scandium into the AlN lattice, creating AlScN alloys with varying scandium concentrations (1-20%). This parameter change increases the piezoelectric coefficient while maintaining the wurtzite structure, thus improving gate control efficiency without sacrificing structural stability
2Power
If high scandium content is introduced to enhance piezoelectric effect, then piezoelectric properties improve, but crystal quality deteriorates due to strain accumulation
Solution Approach 1:
The patent applies local quality by creating a graded scandium distribution within the ferroelectric layer. The scandium content varies spatially, with higher concentrations near the AlScN/Si interface where strain relief is needed, and lower concentrations in regions where piezoelectric performance is prioritized. This gradient structure locally manages strain while maintaining overall crystal quality and enhancing piezoelectric effect
Solution Approach 2:
The patent segments the ferroelectric layer into multiple sub-layers with different scandium contents (e.g., first AlScN layer with 5-15% Sc, second AlScN layer with 10-20% Sc). This segmentation allows each layer to be optimized for specific functions: lower scandium layers maintain crystal quality, while higher scandium layers provide enhanced piezoelectric effect, collectively resolving the contradiction
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 crystal quality of the ferroelectric layers, enabling more efficient gate control and potentially leading to programmable multilevel conductance states for improved data storage and device performance.
Implementation Method 1
A first material layer is formed on a silicon base material, wherein the first material layer includes crystalline aluminum nitride or aluminum scandium nitride (AlScN) with a first Sc content. A second material layer is formed on the first material layer, wherein the second material layer includes aluminum scandium nitride (AlScN) with a second Sc content higher than the first Sc content
Implementation Method 2
The development of aluminum scandium nitride (AlScN) alloys, where scandium is introduced into aluminum nitride (AlN) to increase piezoelectric effects
Data Source
AI summary
A method of fabricating a semiconductor device is described. A first material layer is formed, wherein the first material layer contains crystalline aluminum nitride or aluminum scandium nitride (AlScN) with a first Sc content. A second material layer is formed on the first material layer, wherein the second material layer contains aluminum scandium nitride (AlScN) with a second Sc content higher than the first Sc content. A third material layer is formed on the second material layer, wherein the third material layer contains aluminum scandium (AlSc).