JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV MEMS DESIGN Previous Question Paper (December - 2020 - R15)

The MEMS industry faces several critical challenges that hinder rapid commercialization and widespread adoption:

• Packaging and Integration: Unlike standard ICs, MEMS devices often require interaction with the environment (e.g., pressure sensors, chemical sensors), making hermetic sealing and protection against harsh environments while maintaining sensitivity extremely difficult.
• Standardization: The lack of standardized manufacturing processes and design tools compared to CMOS technology leads to high development costs and longer time-to-market.
• Reliability and Testing: MEMS devices involve moving mechanical parts, which introduces wear, fatigue, and stiction. Testing these devices at the wafer level is complex and expensive.
• Design Complexity: MEMS design requires multi-physics simulation (coupling mechanical, electrical, thermal, and fluidic domains), which is computationally intensive and requires specialized expertise.
• Cost of Fabrication: Small production volumes often prevent the economies of scale seen in the semiconductor industry, making the initial investment in fabrication facilities a significant barrier.

The fabrication of microelectronic devices follows a repetitive sequence of additive and subtractive processes to build complex 3D structures on a silicon substrate. The key process sequences include:

1. Substrate Preparation: Cleaning the silicon wafer to remove contaminants and growing an initial layer (e.g., thermal oxidation) to provide an insulating base.
2. Photolithography: Applying a light-sensitive material (photoresist), exposing it to UV light through a mask, and developing it to transfer the geometric pattern onto the wafer.
3. Etching: Removing material from unprotected areas. This is divided into Wet Etching (isotropic, using chemicals) and Dry Etching (anisotropic, using plasma/reactive ions) to achieve precise vertical profiles.
4. Deposition: Adding thin films of material using techniques like Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), or Sputtering.
5. Doping: Introducing impurities into the silicon via Ion Implantation or Diffusion to modify the electrical conductivity of specific regions.
6. Metallization: Depositing metal layers (usually aluminum or copper) to create interconnects between components.
7. Passivation: Depositing a final protective layer to prevent environmental degradation of the fabricated device.