MEMS Acoustic Transducer Substrate Doping for Noise Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
MEMS devices, particularly capacitive devices like acoustic transducers, suffer from noise and variations in sensitivity due to parasitic capacitance caused by variations in the depletion layer of the Metal Insulator Semiconductor (MIS) structure, which is influenced by factors such as light and temperature changes.
Innovation Solution
A MEMS device is designed with a semiconductor substrate containing N-type majority carriers, where the semiconductor substrate has a region with a higher concentration of N-type impurities, preventing the formation of a depletion layer and thus reducing noise and sensitivity variations by balancing interface charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a semiconductor substrate is used as a support substrate for MEMS devices, then mass production and utilization of semiconductor manufacturing processes are enabled, but parasitic capacitance is formed due to MIS structure, causing noise and sensitivity variations
Solution Approach 1:
The patent changes the electrical parameters of the semiconductor substrate by forming a highly doped region with specific resistivity (10^-3 to 10^-6 ohm·cm) to alter the electrical characteristics and eliminate depletion layer formation, thereby resolving the parasitic capacitance issue while maintaining mass production capability
Solution Approach 2:
The patent converts the inherently conductive nature of semiconductor material, which causes parasitic capacitance, into a benefit by creating a highly doped region that actively suppresses depletion layer formation. The same electrical properties that cause the problem are leveraged to prevent the problem through controlled high doping
2Stability of the object's composition
If a depletion layer is formed in the MIS structure, then interface charge is balanced, but the width of the depletion layer varies with light and temperature, causing noise and sensitivity variations
Solution Approach 1:
The patent applies preliminary anti-action by pre-forming a highly doped region in the semiconductor substrate before device operation. This pre-established high-concentration doping region proactively prevents depletion layer formation under subsequent light or temperature variations, eliminating the root cause of noise and sensitivity variations
Solution Approach 2:
The patent fundamentally changes the doping concentration parameter in the semiconductor substrate from typical levels to very high levels (10^-3 to 10^-6 ohm·cm resistivity), which alters the electrical behavior to prevent depletion layer formation and its associated noise issues
3Adaptability or versatility
If the width of the depletion layer is modulated by light or temperature changes, then carrier generation and annihilation occur, but this causes periodic variation in parasitic capacitance magnitude, leading to noise
Solution Approach 1:
The patent changes the doping concentration parameter to extremely high levels, which fundamentally alters the response to light and temperature. The high carrier concentration from heavy doping prevents depletion layer formation, thereby eliminating the mechanism that converts environmental variations into noise-generating capacitance modulation
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 design significantly reduces noise and sensitivity variations in MEMS devices by preventing the formation of a depletion layer, leading to improved S/N ratio characteristics and stability across different environmental conditions.
Implementation Method 1
a MIS (Metal Insulator Semiconductor) structure is readily formed to act as a parasitic capacitor
Implementation Method 2
a depletion layer is formed in the semiconductor substrate. The depletion layer acts as a portion of parasitic capacitance
Data Source
AI summary
A MEMS device includes a first insulating film formed on a semiconductor substrate, a vibrating film formed on the first insulating film, and a fixed film above the vibrating film with an air gap being interposed therebetween. The semiconductor substrate has a region containing N-type majority carriers. A concentration of N-type majority carriers in a portion of the semiconductor substrate where the semiconductor substrate contacts the first insulating film, is higher than a concentration of N-type majority carriers in the other portion of the semiconductor substrate.