CMUT Dielectric Isolation Layer Using High-k ALD
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Solution Overview
Problem
Capacitive micro-machined ultrasound transducers (CMUTs) face limitations in performance due to high operating voltage and low output pressure, primarily attributed to the use of ONO dielectric isolation layers, which have limitations in thickness and dielectric constant, leading to charging issues and reduced stability over time.
Innovation Solution
The use of a dielectric isolation layer comprising an oxide layer sandwiched between high-k layers, specifically Aluminum Oxide and Hafnium Oxide, deposited using Atomic Layer Deposition (ALD), which enhances the dielectric constant and reduces charging, thereby improving operating voltage and output pressure while maintaining stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ONO dielectric isolation layer is used, then charging issue is solved, but dielectric constant is limited (5-7) and thickness is limited (about 250 nm), resulting in high operating voltage and low output pressure
Solution Approach 1:
The patent uses a composite dielectric isolation layer consisting of multiple materials (oxide, nitride, and high-k material) instead of a single ONO layer. This composite structure combines the charging protection properties of oxide-nitride-oxide with the high dielectric constant of materials like hafnium oxide or tantalum oxide, achieving both charging stability and high output pressure
Solution Approach 2:
The patent changes the dielectric constant parameter of the isolation layer by introducing high-k materials with dielectric constants significantly higher than traditional ONO layers. This parameter change allows for thinner effective dielectric thickness while maintaining charging protection, thereby increasing output pressure without sacrificing reliability
2Reliability
If ONO dielectric isolation layer is used, then charging issue is solved, but operating voltage is rather high
Solution Approach 1:
The composite dielectric structure combines oxide-nitride-oxide layers for charging protection with high-k material layers for enhanced capacitance. This allows the transducer to operate at lower voltages while maintaining the charging stability provided by the oxide-nitride-oxide configuration
Solution Approach 2:
By changing the dielectric constant parameter through high-k materials, the patent reduces the operating voltage requirement. The higher dielectric constant increases the capacitance of the isolation layer, allowing it to maintain electrical isolation and charging protection at lower voltage levels
3Power
If dielectric isolation layer thickness is reduced to improve performance, then operating voltage decreases, but breakdown voltage requirement increases
Solution Approach 1:
The patent uses composite dielectric layers where high-k materials provide both high dielectric constant and high breakdown voltage characteristics. The oxide-nitride-oxide structure provides additional electrical isolation, creating a multi-layer composite that simultaneously achieves thin effective thickness for high output pressure while maintaining high breakdown voltage tolerance
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 configuration significantly improves CMUT performance by reducing operating voltage, increasing output pressure, and stabilizing the ultrasound output over time, with the ALD process allowing for precise control of layer properties and interfaces, resulting in a more efficient and reliable transducer.
Implementation Method 1
The terms 'depositing a first electrode layer on a substrate, depositing a first dielectric film on the first electrode layer, depositing a sacrificial layer on the first dielectric film... wherein the depositing steps are performed by Atomic Layer Deposition
Implementation Method 2
the first dielectric film and/or the second dielectric film comprises a first layer comprising an oxide, a second layer comprising a high-k material having a dielectric constant equal to 8 or more
Data Source
Figure 1a~1h
Figure 1i~1j
Figure 2a~2c
AI summary
The present invention relates to a method of manufacturing a capacitive micro- machined transducer (100), in particular a CMUT, the method comprising depositing a first electrode layer (10) on a substrate (1), depositing a first dielectric film (20) on the first electrode layer (10), depositing a sacrificial layer (30) on the first dielectric film (20), the sacrificial layer (30) being removable for forming a cavity (35) of the transducer, depositing a second dielectric film (40) on the sacrificial layer (30), and depositing a second electrode layer (50) on the second dielectric film (40), wherein the first dielectric film (20) and/or the second dielectric film (40) comprises a first layer comprising an oxide, a second layer comprising a high-k material, and a third layer comprising an oxide, and wherein the depositing steps are performed by Atomic Layer Deposition. The present invention further relates to a capacitive micro-machined transducer (100), in particular a CMUT, manufactured by such method.