MEMS and Sensors Overview

• Optical stimulus is best suitable for quantities like refractive index, reflectivity, and absorption in sensors.
• A sensor acquires a physical parameter and converts it into a signal suitable for processing.
• MEMS stands for Micro Electro Mechanical Systems.
• The process steps in Silicon boule growth technique are:
  • Melting of polysilicon
  • Introduction of seed crystal
  • Beginning of crystal growth
  • Crystal pulling
  • Formation of crystal
• Thermal Oxidation is not a physical vapor deposition technique.
• Extracellular and intracellular matrices are not responsible for giving nutrition to the cells".
• "Ex vivo" means study outside the living body, and "in vivo" means study inside the living body.
• In microfluidic chips, CD4 cells are called helper cells, and CD8 cells are killer cells.
• A desired characteristic of a sensor is low power consumption.
• Gas sensors can be used to detect VOCs exhaled from breath.
• The four basic components of MEMS are microelectronics, microsensors, micro actuators, and microstructures.
• The "Class" number of a clean room denotes the number of particles per cubic feet allowed inside the facility.
• Understanding breath signatures using VOC sensors is a non-invasive way of determining disease.
• An incubator is used to maintain the temperature and humidity levels for appropriate growth and preservation of cell and tissue culture.
• An inverted microscope is generally used for observing cells and organisms in culture, in petri dishes, flasks, or microplates.
• VOC stands for Volatile Organic Compound.
• TCOs (like indium tin oxide, zinc oxide, tin oxide) used as sensing material refers to Transparent Conducting Oxides.
• Piezo-electric sensors accumulate charge in response to mechanical force while piezo-resistive sensors cause a change in resistance in response to mechanical force.
• For metals, resistivity increases and for semiconductors, resistivity decreases when temperature is increased.
• Silicon or glass substrates are stored in vacuum in desiccators to avoid dust particles and other gases from contaminating the substrate.
• PPE stands for Personal Protective Equipment in the context of cleanrooms.
• In microfabrication facilities, desiccators are used for storing substrates in vacuum.
• During the video demonstration, the impedance analyzer was not performing a two-probe measurement which is more accurate than a four probe measurement.
• Class 2 biosafety cabinet provides product, personnel, and environmental protection.
• In photolithography, soft bake is not performed at 50 degrees centigrade for 1 minute.
• Nichrome can be used to fabricate microheaters.
• Acetone is used as a photoresist stripper.
• In wet etching, the etch rate is dependent on crystallographic orientation of the substrate, and is anistropic.
• Deep reactive ion etching does not enable very low aspect ratio etches to be performed into silicon substrates.
• BHF is used as the etchant of silicon dioxide.

Assignment 4

• For SU-8, soft bake is performed at 65 degrees centigrade.
• The proper order for the processes related to photolithography:
  • Wafer Cleaning
  • Primer coating
  • Soft bake
  • Photoresist coating
  • Alignment
  • Exposure
  • Development
• Acetone is used as a photoresist stripper.
• Cell lysis will occur, and the conductivity of the chip will increase when a drug is found effective.
• Silicone elastomer and curing agent were used in a 10:1 ratio to prepare PDMS.
• Matrigel acts as an extracellular matrix for cells.
• IDE stands for Integrated Development Environment.
• BHF is used for etching silicon dioxide during the fabrication processes.
• Chrome is deposited before gold for strong adhesion of gold to the substrate when fabricating interdigitated electrodes.
• The optimum temperature and duration for curing the PDMS mold is 70 degrees centigrade for 1 hour.

Assignment 5

• Silicon dioxide can act as a selective mask against diffusion at high temperatures.
• The flow of COMSOL Multiphysics simulation modelling:
  • Make geometry
  • Add materials
  • Apply physics conditions
  • Choose type of study
  • Post process results
• Miller indices describe the orientation of different crystal planes in the basic unit cell.
• Correct statements regarding thermal oxidation:
  • Room temperature silicon in air creates a very thin layer of "native oxide".
  • Wet oxidation is faster than dry oxidation.
• A quarter wave plate converts linearly polarized light to circularly polarized light in an ellipsometer.
• The angle between primary and secondary flats for <100> p-type silicon wafer is 90 degrees.
• Evaporation and Sputtering are two different types of physical vapor deposition techniques.
• Shape memory alloy is a type of ferroelastic material.
• There isn't a secondary flat in <111> p-type silicon wafer.
• Regarding the MQ-3 gas sensor:
  • It is based on the principle of redox reaction.
  • Tin oxide acts as the gas sensing layer.
  • Nickel chromium alloy is the heating element.

Assignment 6

• Biosafety hood cannot be disinfected by UV or steam sterilization.
• In the fabrication process, acetone dip is performed to remove photoresist.
• An additional signal conditioning circuit is needed between the temperature sensor and ADC to improve resolution (each level height).
• Spin-coated photoresist thickness is independent of spin coater rotation speed.
• The flow of COMSOL Multiphysics simulation should be:
  • Make geometry
  • Add materials
  • Apply physics conditions
  • Choose type of study
  • Post process results
• The angle between primary and secondary flats for <100> p-type silicon wafer is 90 degrees.
• HEPA filter stands for High-Efficiency Particulate Air filter.
• The resolution of an 8-bit ADC working at a reference voltage of 3 V is 11.72 V
• The processes related to photolithography in the correct order:
  • Wafer Cleaning
  • Primer coating
  • Soft bake
  • Photoresist coating
  • Alignment
  • Exposure
  • Development
  • Hard bake
• The "Class” number of a clean room denotes the number of particles and not people per cubic feet allowed inside the facility.