Topside Boss Pressure Sensor Using DRIE Etching
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Solution Overview
Problem
Existing pressure sensors face challenges in achieving high sensitivity and linearity due to the use of thick bosses, which are difficult to align and increase the sensor's mass, affecting accuracy and compatibility with CMOS manufacturing processes.
Innovation Solution
The use of deep reactive-ion etching (DRIE) or plasma etching to form a topside boss and cavity with orthogonal sides, allowing for reduced mass, improved alignment, and compatibility with p-doped substrates, enabling smaller die size and enhanced manufacturing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thick boss is formed in the cavity below the diaphragm to increase sensitivity and linearity, then sensitivity and linearity are improved, but the boss mass increases causing stress on the diaphragm during acceleration and varying stress due to gravity
Solution Approach 1:
The boss is extracted from the cavity region and repositioned to the topside of the diaphragm. This removes the mass problem while retaining the stress concentration function, as the boss now sits above rather than below the diaphragm, eliminating gravitational and acceleration-induced stress on the diaphragm.
Solution Approach 2:
Instead of forming the boss from the cavity side (bottom-up), the invention inverts the approach by forming the boss from the topside (top-down). This inversion allows the boss to be aligned with topside features and eliminates the mass-related stress problems while maintaining the stress concentration effect for sensitivity enhancement.
2Measurement precision
If a thick boss is formed in the cavity below the diaphragm to increase sensitivity and linearity, then sensitivity and linearity are improved, but alignment with features such as Wheatstone bridge on the topside of the diaphragm becomes difficult
Solution Approach 1:
The boss is extracted from the cavity region and repositioned to the topside of the diaphragm. This allows the boss to be precisely aligned with topside features such as the Wheatstone bridge during a single manufacturing process, eliminating alignment difficulties between bottomside and topside features.
3Ease of manufacture
If KOH etch is used to form the cavity and boss, then the boss can be formed, but the cavity has sloped sides consuming greater area and increasing sensor size
Solution Approach 1:
The chemical KOH etching process is replaced with a physical sputtering process. This substitution allows for formation of orthogonal cavity sides without requiring the sloped-side KOH etch, reducing the die area while still enabling boss formation through topside trench etching.
4Ease of manufacture
If KOH etch is used to form the cavity and boss, then the boss can be formed, but n-doped silicon wafer is needed which is incompatible with most CMOS processes based on p-doped silicon wafer
Solution Approach 1:
The chemical KOH etching process requiring n-doped silicon is replaced with physical sputtering that works with p-doped silicon wafers. This substitution enables compatibility with standard CMOS manufacturing processes while still allowing boss and cavity formation through the topside trench etching approach.
Solution Approach 2:
The doping type parameter of the silicon wafer is changed from n-doped (required for KOH etch) to p-doped (compatible with CMOS). The etching method parameter is simultaneously changed from chemical etch to physical sputter etch, allowing the process to work with the desired p-doped substrate for CMOS compatibility.
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 pressure sensors with increased sensitivity and linearity, reduced susceptibility to gravity and acceleration, and compatibility with conventional CMOS technologies, leading to more accurate and compact pressure measurements.
Implementation Method 1
The cavity may be formed using a deep reactive-ion etch
Implementation Method 2
plasma etching to form a topside boss and cavity with orthogonal sides
Implementation Method 3
Pressure, either from above the diaphragm or below in a cavity, deflects the diaphragm and its sensors. This deflection, and hence the pressure, can be measured by utilizing the piezo-resistive effect.
Data Source
Figure 1a~1
Figure 2
Figure 3a~3
AI summary
Pressure sensors having a topside boss and a cavity formed using deep reactive-ion etching (DRIE) or plasma etching. Since the boss is formed on the topside, the boss is aligned to other features on the topside of the pressure sensor, such as a Wheatstone bridge or other circuit elements. Also, since the boss is formed as part of the diaphragm, the boss has a reduced mass and is less susceptible to the effects of gravity and acceleration. These pressure sensors may also have a cavity formed using a DRIE or plasma etch. Use of these etches result in a cavity having edges that are substantially orthogonal to the diaphragm, such that pressure sensor die area is reduced. The use of these etches also permits the use of p-doped wafers, which are compatible with conventional CMOS technologies.