MEMS Proof Mass Stopper with Silicon Layer
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Solution Overview
Problem
Conventional MEMS devices face issues with stiction between movable parts and metal surfaces, leading to reduced production yield and reliability due to their large surface area to volume ratio, which affects their performance in sensing physical quantities.
Innovation Solution
Incorporating a stopper with a silicon-based layer having a rough surface and conductivity, disposed directly under the proof mass and spaced apart from it, to prevent stiction with the interconnect layer, which is fabricated using conductive and dielectric layers stacked alternately in the MEMS device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional MEMS device structure is used with metal surfaces, then the device can be manufactured with standard processes, but stiction occurs between the proof mass and metal surface leading to reduced reliability and production yield
Solution Approach 1:
A stopper structure is introduced as an intermediary element between the proof mass and the metal surface. The stopper includes a bottom portion made from one of the conductive layers of the interconnect layer, and a silicon-based layer disposed on the bottom portion. This intermediary structure prevents direct contact between the proof mass and metal surface, thereby eliminating stiction while maintaining electrical connectivity through the conductive layer integration.
Solution Approach 2:
The stopper is constructed using composite materials combining a conductive layer (from the interconnect layer stack) and a silicon-based layer. This composite structure provides both electrical conductivity through the metal layer and mechanical protection against stiction through the silicon-based layer, which has appropriate surface properties to prevent adhesion with the proof mass.
2Volume of moving object
If the proof mass is positioned close to the interconnect layer for compact design, then device footprint is reduced, but mechanical damage may occur under mechanical shocks
Solution Approach 1:
The stopper structure is positioned between the proof mass and the interconnect layer to provide beforehand cushioning. During normal operation, the stopper maintains a small gap for compact design, but during mechanical shocks, the stopper absorbs impact energy and prevents direct contact between the proof mass and the interconnect layer, thereby protecting against mechanical damage.
3Reliability
If electrostatic charges accumulate on metal surfaces, then electrical functionality is maintained, but stiction is generated reducing production yield
Solution Approach 1:
The silicon-based layer of the stopper acts as an intermediary that prevents direct electrostatic interaction between the proof mass and the metal surface. While the conductive layer can still manage electrical charges, the silicon-based layer prevents these charges from causing stiction by eliminating direct metal-to-proof-mass contact, thereby resolving the harmful effect of charge accumulation.
Data Source
AI summary
A micro-electro-mechanical system (MEMS) device includes a first substrate, an interconnect layer, a MEMS device layer, a stopper and a second substrate. The interconnect layer is disposed on the first substrate and includes a plurality of conductive layers and a plurality of dielectric layer stacked alternately. The MEMS device layer is bonded on the interconnect layer and includes a proof mass. The stopper is disposed directly under the proof mass and spaced apart from the proof mass, where the stopper is surrounded by a portion of the interconnect layer, and the stopper includes a bottom portion constructed of one of the plurality of conductive layers, and a silicon-based layer disposed on the bottom portion. The second substrate includes a cavity and is bonded on the MEMS device layer.