Polycrystalline silicon micromachining: a new technology for integrated sensors

Area of Science:

• Materials Science
• Microelectromechanical Systems (MEMS)
• Integrated Circuit Technology

Background:

• Polycrystalline silicon (poly-Si) is a key material for microfabrication.
• Internal stress in poly-Si films limits microstructure dimensions.
• Annealing can effectively reduce this internal stress.

Purpose of the Study:

• To describe the fabrication of an integrated vapor sensor using poly-Si micromachining.
• To evaluate the material properties of poly-Si for micro-device applications.
• To explore the potential of poly-Si micromachining for pressure transducers.

Main Methods:

• Selective etching of a sacrificial oxide layer to release poly-Si microstructures.
• Annealing of poly-Si films to reduce internal compressive stress.
• Fabrication of a resonant poly-Si microbridge integrated with NMOS circuitry.
• Frequency response measurements to characterize the microbridge's mechanical properties.

Main Results:

• Successful fabrication of an integrated vapor sensor with a resonant poly-Si microbridge.
• Frequency response data indicate a Young's modulus of 4 x 10^10 Nm-2 for poly-Si.
• This Young's modulus is significantly lower than that of crystalline silicon.
• Identified poly-Si micromachining as a viable technique for pressure transducer fabrication.

Conclusions:

• Poly-Si micromachining is a versatile and IC-compatible technique for microfabrication.
• Annealing is crucial for managing internal stress in poly-Si microstructures.
• The determined Young's modulus provides critical data for poly-Si device design.
• Further research is needed to optimize poly-Si micromachined pressure transducers.