Dielectric Coupling in CMOS-MEMS Out-of-Plane Sensors
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Solution Overview
Problem
Micro-electro-mechanical system (MEMS) devices bonded to complementary metal-oxide semiconductor (CMOS) layers using metal eutectic bonding exhibit non-linear behavior under external loads, leading to undesirable false signals due to the presence of metal in the mechanical connection, which is undesirable for accurate sensing.
Innovation Solution
A micro-electro-mechanical sensor device design that uses a dielectric coupling between the MEMS actuator layer and the cover layer, with a spring and anchor connecting the MEMS layer to the CMOS substrate, eliminating metal from the mechanical connection and incorporating a CMOS sensing element to detect stimuli such as barometric pressure, humidity, and acceleration, while using eutectic bonds for electrical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal eutectic bonding is used to connect MEMS layers to CMOS layers, then mechanical connection and electrical coupling are achieved, but non-linear behavior occurs under external loads causing false signals
Solution Approach 1:
The patent removes metal from the mechanical connection path between MEMS and CMOS layers. The sense electrode is mechanically decoupled by introducing a dielectric material, while electrical coupling is maintained through separate metal pathways. This extraction of metal from the load-bearing path eliminates the non-linear behavior that causes false signals.
Solution Approach 2:
A dielectric material is introduced as an intermediary between the sense electrode and the structural connection. This dielectric layer acts as a mediator that provides mechanical support and electrical isolation, allowing the sense electrode to remain electrically connected to CMOS while being mechanically supported without metal, thereby preventing non-linear signal behavior.
2Measurement precision
If metal is used in the mechanical connection across the sense gap, then electrical coupling is achieved, but false signals are generated under external loads
Solution Approach 1:
Metal is extracted from the mechanical connection across the sense gap. The sense electrode is supported by a dielectric material instead of metal, eliminating the source of non-linear behavior. Electrical coupling is maintained through separate metal pathways that do not bear mechanical loads, preserving sensing accuracy.
Solution Approach 2:
The connection function is segmented into separate pathways: one for mechanical support (dielectric material) and one for electrical coupling (metal pathways). This segmentation allows each function to be optimized independently, with the dielectric providing linear mechanical support and metal providing electrical connectivity without bearing loads.
3Reliability
If a dielectric is used to couple the actuator layer to the cover layer, then metal is eliminated from mechanical connections, but electrical coupling pathways must be established separately
Solution Approach 1:
The metal layers in the CMOS and MEMS structures serve dual functions: providing electrical connectivity and structural support. By utilizing existing metal pathways for electrical coupling and introducing dielectric for mechanical support, the design avoids adding separate dedicated pathways, reducing overall complexity while achieving both functions.
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 false signals from external loads by eliminating metal from the mechanical connection, enabling accurate sensing of stimuli and stable output signals, improving the reliability of MEMS devices.
Implementation Method 1
a portion of the actuator layer is coupled to the cover layer via a dielectric
Implementation Method 2
the MEMS device layer is connected to a complementary metal-oxide-semiconductor (CMOS) substrate layer via a spring and an anchor
Implementation Method 3
Metal, like aluminum-germanium (Al—Ge) used for eutectic bonding of micro-electro-mechanical system (MEMS) devices to complementary metal-oxide semiconductor (CMOS) layers
Implementation Method 4
The out-of-plane sense element can be a variable capacitor between the actuator layer and the cover layer
Data Source
AI summary
A micro-electro-mechanical system sensor device is disclosed. The sensor device comprises a micro-electro-mechanical system (MEMS) layer, comprising: an actuator layer and a cover layer, wherein a portion of the actuator layer is coupled to the cover layer via a dielectric; and an out-of-plane sense element interposed between the actuator layer and the cover layer, wherein the MEMS device layer is connected to a complementary metal-oxide-semiconductor (CMOS) substrate layer via a spring and an anchor.