CMUT Protrusion Cavity Reduces Pull-in Voltage
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Solution Overview
Problem
Capacitive micro-machined ultrasonic transducers (CMUTs) face issues with charge accumulation due to high pull-in voltage, which affects device performance and resonant frequency tuning, especially in broadband applications, and increased charge accumulation occurs during membrane contact with the cavity bottom surface due to friction.
Innovation Solution
Incorporating a protrusion within the sealed cavity reduces the moving distance of the movable membrane and the area of contact, thereby lowering the required pull-in voltage and minimizing charge accumulation, with the protrusion's profile designed to reduce contact area and friction-induced charge accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the movable membrane is designed to contact the cavity bottom surface, then the device structure is simplified, but charge accumulation increases due to friction
Solution Approach 1:
The patent extracts the problematic contact surface from the cavity bottom by introducing a protrusion structure. The protrusion is separated from the movable membrane, eliminating direct contact between the membrane and the cavity bottom surface, thereby removing the source of friction-induced charge accumulation while maintaining structural simplicity.
Solution Approach 2:
The protrusion acts as an intermediary element between the movable membrane and the cavity bottom surface. Instead of direct contact between the membrane and the flat cavity bottom, the protrusion provides a controlled interaction point that reduces contact area and minimizes friction, thus reducing charge accumulation.
2Adaptability or versatility
If the pull-in voltage is increased to achieve broadband operation, then resonant frequency tuning capability is improved, but charge accumulation increases
Solution Approach 1:
The patent converts the harmful effect of high pull-in voltage (which causes charge accumulation) into a benefit by using the protrusion structure. The protrusion allows the membrane to achieve the necessary displacement for broadband operation and resonant frequency tuning while minimizing the contact area, thus reducing charge accumulation even at high voltages.
3Use of energy by moving object
If the moving distance of the movable membrane is reduced, then pull-in voltage is lowered, but the cavity space utilization is reduced
Solution Approach 1:
The patent introduces a vertical dimension element (the protrusion) into the cavity structure. By positioning the protrusion at a specific height within the cavity, the membrane's moving distance is effectively reduced from the full cavity depth to the distance to the protrusion top surface, lowering the pull-in voltage while still utilizing the cavity's vertical space efficiently.
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 solution effectively reduces the pull-in voltage by up to 25% and minimizes charge accumulation, enhancing the performance of CMUT cells by maintaining lower charge levels and improving resonant frequency tuning capabilities.
Implementation Method 1
Capacitive micro-machined ultrasonic transducers (CMUTs) face issues with charge accumulation due to high pull-in voltage
Implementation Method 2
increased charge accumulation occurs during membrane contact with the cavity bottom surface due to friction
Data Source
AI summary
A method for forming a semiconductor structure includes following operations. An interconnect structure is formed over a substrate. The interconnect structure includes a top conductive layer. A dielectric structure is formed over the interconnect structure. The dielectric structure is patterned to simultaneously form a cavity and a protrusion in the cavity. A MEMS substrate is bonded to the dielectric structure to seal the cavity. The protrusion is separated from the MEMS substrate.