CMOS MEMS Microphone Undoped Polysilicon Insulator
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Solution Overview
Problem
Conventional CMOS MEMS microphones face short-circuiting issues due to the lack of a barrier between the backplate and diaphragm, and existing etch stop layers are not suitable, leading to inefficiencies in fabrication and system integration.
Innovation Solution
A CMOS MEMS microphone is fabricated using a patterned undoped polysilicon layer to separate the doped polysilicon layer from the metal electrode, preventing short-circuiting and enhancing the efficiency of the microphone by using undoped polysilicon as an insulator between the doped polysilicon vibration diaphragm and the metal electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If no blocker is placed between the backplate and diaphragm to maintain a simple structure, then device complexity is reduced, but the backplate and diaphragm are easily short-circuited when the diaphragm vibrates, worsening reliability
Solution Approach 1:
An undoped polysilicon layer is introduced as an intermediary between the doped polysilicon diaphragm and the metal backplate. This undoped polysilicon layer serves as an electrical insulator that prevents short-circuits while maintaining mechanical coupling for vibration transmission, thus resolving the contradiction between structural simplicity and reliability
Solution Approach 2:
The patent applies different doping characteristics to different regions: the diaphragm uses doped polysilicon for conductivity and mechanical properties, while the blocking layer uses undoped polysilicon for electrical insulation. This local differentiation of material properties enables both vibration transmission and short-circuit prevention without adding complex structures
2Manufacturing precision
If an etch stop layer is used to form a cavity, then manufacturing precision is improved, but the etch stop layer must be made of materials not suitable for standard CMOS processes (e.g., SiN instead of polysilicon), worsening ease of manufacture
Solution Approach 1:
The undoped polysilicon layer serves multiple functions: it acts as an etch stop layer for precise cavity formation, provides electrical insulation to prevent short-circuits, and maintains compatibility with standard CMOS fabrication processes. This multi-functionality eliminates the need for specialized materials like SiN while achieving the same manufacturing precision
3Area of stationary object
If the horizontal position of the metal electrode overlaps with the doped polysilicon layer, then device area is reduced, but electrostatic forces are vertically formed between the metal electrode and doped polysilicon layer causing attraction and short-circuit events, worsening reliability
Solution Approach 1:
The undoped polysilicon layer is positioned between the metal electrode and doped polysilicon diaphragm with horizontal offset. This intermediary layer blocks vertical electrostatic attraction forces while allowing the device to maintain compact area, preventing short-circuit events caused by electrostatic attraction
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 effectively avoids short-circuiting and improves the efficiency of the microphone by using undoped polysilicon as an insulator, allowing for better system integration and reduced fabrication errors.
Implementation Method 1
uses the undoped polysilicon of a patterned polysilicon layer to separate a doped polysilicon layer from a metal electrode, thereby avoiding short-circuiting
Implementation Method 2
The diaphragm 12 vibrates when air vibrates to transmit sound pressure to the diaphragm 12
Implementation Method 3
electrostatic forces be vertically formed between the metal electrode and the patterned doped polysilicon layer such that the metal electrode and the patterned doped polysilicon layer attract to cause a short-circuit event
Data Source
AI summary
A complementary metal-oxide-semiconductor (CMOS) micro electro-mechanical system (MEMS) microphone and a method for fabricating the same are disclosed. Firstly, a CMOS device including a semiconductor substrate, a first oxide insulation layer, a doped polysilicon layer, a second oxide insulation layer, a patterned polysilicon layer, and a metal wiring layer from bottom to top. The metal wiring layer is formed on the second oxide insulation layer. The patterned polysilicon layer includes undoped polysilicon. Then, a part of the metal wiring layer is removed to form a metal electrode and the semiconductor substrate is penetrated to have a chamber and expose the first oxide insulation layer, thereby forming a MEMS microphone.