Vertical Sidewall Pressure Sensor via DRIE Etching
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Solution Overview
Problem
Conventional silicon pressure sensors have large die sizes due to sloped frame sidewalls, limiting the number of sensors that can be fabricated on a wafer and increasing production costs, while also facing challenges in sensitivity variability and stress distribution.
Innovation Solution
The development of pressure sensors with substantially vertical frame sides orthogonal to the diaphragm, achieved through Deep Reactive Ion Etching (DRIE) or other MEMS micro-machining techniques, allowing for adjustable sensitivity using a limited number of masks and processing steps, and incorporating a cross-shaped backside opening with rounded corners to reduce stress and breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional KOH etching is used to form the backside cavity, then the manufacturing process is simple, but the frame sidewalls have a 54.7 degree slope that increases die size
Solution Approach 1:
The patent changes the etching parameters by switching from isotropic KOH etching to anisotropic DRIE etching, which produces vertical sidewalls instead of sloped ones. This parameter change in the etching process directly reduces the die size by eliminating the lateral etch component that creates the 54.7 degree slopes.
Solution Approach 2:
The patent substitutes the chemical etching mechanism (KOH) with a plasma-based DRIE process that uses alternating chemical etching and physical polymer deposition. This substitution enables vertical sidewall formation through controlled anisotropic etching, resolving the contradiction between manufacturing simplicity and die size reduction.
2Manufacturing precision
If the backside opening width is increased to accommodate sloped sidewalls, then the etching process can be completed, but the die length increases significantly
Solution Approach 1:
The patent changes the geometric parameters of the etched cavity by using DRIE to create vertical sidewalls. This eliminates the need for additional lateral space that would otherwise be required to accommodate sloped sidewalls, thereby reducing die length while maintaining complete cavity formation.
3Length of stationary object
If the number of masks and processing steps is increased to achieve vertical sidewalls, then the die size is reduced, but the manufacturing complexity increases
Solution Approach 1:
The patent makes the DRIE process multi-functional by using it to simultaneously achieve vertical sidewalls, precise depth control, and high aspect ratio cavity formation. This single process replacement for multiple conventional steps reduces overall manufacturing complexity while achieving die size reduction.
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 significantly reduces sensor die size, enabling the fabrication of a high-density array of sensors on a wafer, making the production cost-effective and allowing for variable sensitivity, while minimizing stress and breakage, thus suitable for applications in portable devices and tire pressure monitoring systems.
Implementation Method 1
These sides, the interior sidewall of a backside cavity, are formed using a Deep Reactive Ion Etch (DRIE) or other Micro-Electro-Mechanical System (MEMS) micro-machining technique.
Data Source
AI summary
Methods and apparatus for an absolute or gauge pressure sensor having a backside cavity with a substantially vertical interior sidewall. The backside cavity is formed using a DRIE etch or other MEMS micro-machining technique. The backside cavity has an opening that is cross shaped, where the dimensions of the cross may be varied to adjust pressure sensor sensitivity. The cross may have one or more rounded corners to reduce peak stress, for example, the interior corners may be rounded. A sensing conductor may be routed over one or more corners including the interior corners to detect breakage.