English 
Chinese Wuxi Silicon Source Technology (SISTC) has introduced a breakthrough fabrication method for MEMS MIC design, utilizing a Multi-Film Thickness (MFT) lithography process to build a novel staircase contour cavity (S-CTC) structure. This innovation promises significant improvements in signal-to-noise ratio (SNR) and sensitivity for next-generation microphones.
Background: Why Structure Matters in MEMS Microphones
MEMS microphones, especially silicon capacitive microphones, have become a critical component in smartphones, IoT devices, and medical applications. Current designs rely on conventional box cavity (BC) structures, where only ~2/3 of the diaphragm contributes effectively to sound sensing, limiting capacitance and SNR performance.
Attempts to overcome this limitation have included gray-scale lithography (GSL), which can fabricate smooth 3D cavity structures. However, GSL remains costly due to ultra-fine mask requirements (SPIE – Grayscale Lithography for 3D Microfabrication).
The MFT Lithography Breakthrough
The Multi-Film Thickness (MFT) mask developed by SISTC replaces the need for multiple etching steps. By using chromium film layers of different thicknesses (0, 4, 14, and 114 nm), a single photolithography exposure achieves the desired 3D staircase structure.
- Single etch step replaces costly multi-step processes
- Achieved capacitance increase: from 2.2 pF → 2.9 pF (~30% improvement)
- Improved SNR and sensitivity without increasing die size or diaphragm fragility
This allows for high-performance MEMS microphones at a cost competitive with today’s mass-market designs.
Learn more about SISTC’s MEMS Microphone Product Line.
Performance and Application Outlook
The enhanced capacitance directly contributes to higher SNR, a critical factor for sound clarity. With smartphones increasingly integrating 3–4 microphones per device, demand for higher SNR solutions continues to grow.
Moreover, this process opens doors for ultra-low-pressure sensing in advanced applications, such as:
- Smartphones & IoT voice interfaces
- Wearable devices requiring always-on microphones
- Medical equipment, including advanced electronic stethoscopes
Competitive Advantage
Compared to traditional box cavity capacitive microphones, the staircase contour cavity (S-CTC) design maximizes diaphragm movement and capacitance, enabling better performance without excessive costs.
The MFT mask approach thus combines the low-cost advantage of binary lithography with the 3D precision of advanced etching processes.
Conclusion
SISTC’s MFT-based MEMS microphone technology represents a key step forward in high-SNR, cost-efficient microphone fabrication. By optimizing capacitance through structural innovation, SISTC enables next-generation MEMS MIC solutions for smartphones, IoT, and healthcare.
Learn more about Wuxi Silicon Source Technology (SISTC) and our ongoing innovations in MEMS MIC and sensor technologies.
