CMUT High-k Dielectric Layers for Low Voltage Operation
Find Innovative SolutionsGenerate Solutions
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 thickness and dielectric constant of ONO dielectric layers, which also lead to charging issues.
Innovation Solution
The method involves depositing all CMUT functional layers using Atomic Layer Deposition (ALD) in a single process sequence, with a 'top-to-bottom' patterning technique to create a pyramid structure, and replacing ONO dielectric isolation layers with high-k materials like Aluminium Oxide or Hafnium Oxide to enhance dielectric constant and reduce operating voltage while increasing output pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ONO dielectric isolation layers are used in CMUT, then charging issues are reduced, but the dielectric constant remains low (5-7) and layer thickness cannot be minimized, resulting in high operating voltage and low output pressure
Solution Approach 1:
The patent changes the dielectric material parameter from conventional ONO (oxide-nitride-oxide) to high-k materials such as barium strontium titanate (BST), lead zirconate titanate (PZT), or tungsten bronzes. This material substitution increases the dielectric constant from 5-7 to values exceeding 100, enabling the capacitor to achieve the same capacitance with thinner layers and thereby reducing operating voltage while maintaining charging stability.
Solution Approach 2:
The patent employs composite dielectric structures combining high-k materials with conductive layers or gradient compositions. For example, BST is combined with platinum electrodes to form a capacitor with enhanced performance, or gradient-composition films are used to optimize both dielectric properties and mechanical stress distribution, achieving low operating voltage without sacrificing reliability.
2Reliability
If ONO dielectric isolation layers are used in CMUT, then charging issues are reduced, but the dielectric layer thickness cannot be minimized, resulting in low output pressure
Solution Approach 1:
By substituting ONO dielectric layers with high-k materials, the patent achieves the same electrical isolation and capacitance function with significantly reduced layer thickness. This thinning of the dielectric layer increases the mechanical compliance of the membrane, allowing greater displacement under the same driving force and thereby increasing acoustic output pressure.
Solution Approach 2:
The patent utilizes the piezoelectric or electrostrictive properties of high-k materials like PZT and BST, which exhibit nonlinear strain responses to electric fields. This enables enhanced membrane curvature and displacement during operation, increasing the acoustic pressure output while maintaining electrical stability.
3Ease of manufacture
If conventional deposition techniques (PECVD, LPCVD) are used for CMUT fabrication, then manufacturing is established, but multiple deposition and patterning steps are required, increasing process complexity
Solution Approach 1:
The patent combines multiple deposition steps into a single atomic layer deposition (ALD) process sequence. The ALD technique enables conformal deposition of high-k dielectric materials and conductive layers in alternating cycles within one continuous process, eliminating the need for separate PECVD/LPCVD deposition and patterning steps, thereby reducing process complexity while maintaining manufacturing feasibility.
4Power
If thin dielectric isolation layers are used to improve CMUT performance, then operating voltage decreases, but electrical breakdown risk increases
Solution Approach 1:
The patent changes the dielectric material from ONO to high-k materials with superior breakdown strength characteristics. Materials like BST and PZT not only provide high dielectric constants but also maintain high breakdown voltages even at reduced thicknesses, enabling thin-layer design without compromising electrical reliability.
Solution Approach 2:
The patent employs composite structures where high-k dielectric layers are combined with conductive shielding layers or gradient-composition buffers. These composite designs distribute electric field stress more uniformly, preventing localized breakdown while maintaining thin overall thickness and low operating voltage.
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 results in improved CMUT performance by lowering the operating voltage and increasing output pressure, while maintaining stability and reducing charge trapping, thereby enhancing receive sensitivity and acoustic output.
Implementation Method 1
The method comprises: 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, depositing a second dielectric film on the sacrificial layer, depositing a second electrode layer on the second dielectric film, wherein the depositing steps are performed by Atomic Layer Deposition
Implementation Method 2
replacing ONO dielectric isolation layers with high-k materials like Aluminium Oxide or Hafnium Oxide to enhance dielectric constant and reduce operating voltage
Implementation Method 3
A CMUT comprises a membrane (or diaphragm), a cavity underneath the membrane, and electrodes forming a capacitor. For receiving ultrasound waves, ultrasound waves cause the membrane to move or vibrate and the variation in capacitance between the electrodes can be detected. Thereby, the ultrasound waves are transformed into a corresponding electrical signal. Conversely, an electrical signal applied to the electrodes causes the membrane to move or vibrate and thereby transmitting ultrasound waves.
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), depositing a second electrode layer (50) on the second dielectric film (40), and patterning at least one of the deposited layers and films (10, 20, 30, 40, 50), 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.