SRI KRISHNA COLLEGE OF ENGINEERING & TECHNOLOGY KUNIAMUTHUR, COIMBATORE. DEPARTMENT OF MECHATRONICS ENGINEERING CLASS SUBJECT STAFF NAME
Unit – I
: IV MCT A and B : MEMS and NEMS :
INTRODUCTION TO FABRICATION TECHNIQUES
2 mark questions 1. Define MEMS. MEMS :MicroElectroMechanical System Any engineering system that performs electrical and and mechanical functions functions with components in micrometers is micrometers is a MEMS. (1 µm = 1/10 of human hair) 2. List any four advantages of Miniaturization. (i)Small systems tend to move or stop more quickly due to low mechanical inertia. It is thus ideal for precision for precision movements and for rapid actuation. actuation. (ii)Miniaturized systems encounter less thermal distortion and mechanical vibration due to low mass. (iii) Miniaturized devices are particularly suited for biomedical and aerospace applications due to their minute sizes and weight. (iv) Less material requirements mean low cost of production and transportation 3. Give any 4 reasons why Silicon is the most widely used substrate material for MEMS. (i) It is mechanically stable and it is feasible to be integrated into electronics on the same substrate (b/c it is a semiconducting material). (ii) Electronics for signal transduction such as the p or n-type piezoresistive can be readily integrated with the Si substrate-ideal for transistors. (iii) Its thermal expansion coefficient is about 8 times smaller than that of steel, and is more than 10 times smaller than that of aluminum. (iv) Silicon shows virtually no mechanical hysteresis. It is thus an ideal candidate material for sensors and actuators. 4. What is the name of the method used for producing Single crystal Silicon? Also write the chemical equation involved. The most commonly used method of producing single-crystal silicon is the Czochralski (CZ) method. Chemical reaction for the process: SiC + SiO2 → Si + CO + SiO 5. List any four Microsystems Fabrication processes. i. Photolithography ii. Ion Implantation
iii. Diffusion iv. Oxidation v. Chemical vapour Deposition vi. Physical vapour Deposition vii. Ethching viii. Deposition by Epitaxy 6. Distinguish between Ion implantation and Diffusion. Ion Implantation Diffusion i. It is a low temperature process It is a high temperature process ii. The profile of the spread of dopant in The profile of the spread of dopant in silicon by ion implantation is narrow silicon by diffusion is wide iii. It is a physical process It is a chemical process 7. Write a note on resists used in Photolithography process. Positive Resists There are two kinds of positive resists: (1) the PMMA (polymethymethacrylate) resists, (2) the two-component DQN resist involving diazoquinone ester (DQ) and phenolic novolak resin (N). In the latter kind, the first component takes about 20-50% by weight in the compound. Positive resists are sensitive to UV lights with the maximum sensitivity at a wavelength of 220 nm. Negative Resists (1) Two-component bis (aryl) azide rubber resists, and (2) Kodak KTFR (azide-sensitized polyisotroprene rubber). Negative resists are less sensitive to optical and x-ray exposures but more sensitive to electron beams. Xylene is the most commonly used solvent for developing negative resists. 8. Define Photolithography? According to Ruska [1987] ,the Photolithography process involves the use of an optical image and a photosensitive film to produce a pattern on a substrate.It is one of the most important steps in microfabrication. 9. Define Doping? The process of adding impure materials to a material of interest is called doping,and the impure materials involved in this process is called dopants.For example,An impure semiconductor is obtained from pure semiconductor by the process of doping. Types of doping are, 1.Diffusion based doping 2.Ion implantation based doping.
10. Write the equation involved in oxidation process(wet and dry). Growing SiO2 with dry O2 in the air, or w et steam by the following two chemical reactions at high temperature: Si (solid) + O2 (gas) → SiO2 (solid) Si (solid) + 2H2O (steam) → SiO2 (solid) + 2H2 (gas) 11. Which is faster among dry and wet oxidation process? Wet Oxidation is faster than dry oxidation 12. Define thin film deposition? Functional materials, conductors and insulators can be incorporated on a wafer through additive deposition process. One such depo sition process is direct transfer of the material from a source to the wafer surface in an atom by atom, layer by layer fashion. Example metal evaporation and metal sputtering. 13. Define Epitaxy ? Epitaxy is the extension of a single crystal substrate by growing a film of the same single crystal material. For example, One may use this p rocess to deposit silicon film over the desired part of the silicon substrate in order to build the thickness of the microstructure. This is one process that is frequently used in microelectronics industry in the production of silicon diode and transistors. 14. What is the use of resists in photolithography process? Resists are used in two primary applications;as etch masks and as lift off masks. In an etch mask process ,the resists is patterned and the substrate is selectively etched through the openings in the resist. In lift off process ,material is deposited on top of the p atterned resist.openings in the resist allow the material to attach itself to the substrate ,while elsewhere it remains on the resist surface. 15. Define E-beam lithography? Electron beam lithography provide the lowest cost ap proach to linewidths significantly less than 1 micro meter. System range from scanning – electron microscopes converted for direct write under the control of a computer ,to full lithographic system with automatic pattern alignment and stitching capability to write over large areas. The basic principle are very similar to those of photolithography .the electron beam replaces the uv illumination as the exposure source , and different types of resists are used than for optical process,but otherwise concept remain the same.
16. what is meant by scanned probe technique? The very high viewing resolution achievable with surface probe instruments such as the atomic force and scanned tunneling microscopes has fastered much effort to develop these as lithographic tools. Functional electronic devices have been successfully built using local oxidation , scratching and resist based lithography using the AFM & STM , minimum linewidth achieved using these techniques are below 20 nano meter. 17. what is meant by Imprint lithography? This approach to nanofabrication was proposed and successfully implemented by S.Y.CHOU as a method for parallel processing of nanoscale structure. A recent development in lithographic patterning that shows great promise is the technique of imprint lithography, in which a temp late is patterned and then etched to create a three dimension relief. 18. State the working principle of CVD.
CVD involves the flow of a gas containing diffused reactants (normally in vapor form) over the hot substrate surface The gas that carries the reactants is called “carrier gas” The “diffused” reactants are foreign material that needed to be deposited on the substrate surface The carrier gas and the reactant flow over the hot substrate surface, the ene rgy supplied by the surface temperature provokes chemical reactions of the reactants that form films during and after the reactions The by-products of the chemical reactions are then let to the vent
19. Write the equation involved in Sputtering process. e- + M →M+ + 2eM: Metal 20. Name the methods available for epitaxial deposition. Vapour Phase Epitaxy Molecular Beam Epitaxy 21. What is the significance of etching? Mention the types of etching. MEMS and microsystems consist of components of 3-dimensional geometry. There are two ways to create 3-dimensional geo metry:
(i)by adding materials at the desired locations of the substrates using vapor deposition techniques, or (ii)by removing substrate material at desired locations using the etching m ethods. 22. What are the reactant vapours used in Epitaxial deposition? Silane (SiH4) Dichlorosilane (SiH2Cl2) Trichlorosilane (SiHCl3) Silicon tetrachloride(SiCl4) 23. What is the advantage of using Low Pressure CVD? How? 1.Excellent purity and uniformity, 2.large wafer capacity
8 MARKS / 16 MARKS 1. What is photolithography? Explain the principle of photolithography in d etail with a neat sketch. 2. With a neat diagram explain in detail about Ion Implantation and Diffusion. 3. Explain in detail about the process of Oxidation. 4. Explain in detail about Thin Film Deposition Techniques. 5. Describe in detail about the CVD process with all the parameters that governs it. 6. Write in detail about Epitaxial deposition. 7. Give a detailed description on E-Beam Lithography and Nano Imprint Lithography. 8. List the different Scanned Probe Techniques. Describe any two in detail with Neat Sketch. 9. Explain in detail about Beam Theory and Plate Theory 10. What is the use of strings and membranes in Microscale? Explain them in detail .
SRI KRISHNA COLLEGE OF ENGINEERING & TECHNOLOGY KUNIAMUTHUR, COIMBATORE. DEPARTMENT OF MECHATRONICS ENGINEERING : IV MCT A and B : MEMS and NEMS :
CLASS SUBJECT STAFF NAME
Unit – II
MACHINING AND TRANSPORT THEORY
2 mark questions 24. What do you mean by micromachining?
The micro fabrication techniques are process related. In micromachining how these processes can be used either individually or an integrated nature in the manufacture of mems and Microsystems products such as micro sensors, accelerometers and actuators. The techniques used to produce these products are called micromachining. 25. Define Bulk micromachining.
Bulk micromachining involves the removal of material from the bulk substrates, usually silicon wafers to form the desired three dimensional geometry of the structure. 26. What is the difference between Bulk micro machining and surface micromachining?
Bulk micromachining in which substrate material is removed by physical or chemical means. The surface micromachining techniques build microstructure by adding materials layer by layer on top of the substrate. 27. Define Isotropic etching.
For substrates made of homogeneous and isotropic materials, the chemical etchants with attack the material uniformly in all directions. This orientation independent-etching is referred to as isotropic etching. 28. Define Wet etching.
Wet etching removes the material selectively through chemical reaction. The material is immersed in a chemical solution, which reacts and subsequently dissolves the portion of the material, which is in contact with the solution. Materials not covered by the masks are etched away by the chemical solution, while those covered by the masks are left undissolved
6. Define Dry etching Dry etching involves the removal of material by gaseous etchants without wet chemicals or rinsing. There are three dry etching techniques: 1. Plasma etching 2. Ion milling 3. Reactive ion etching 7. What are the mechanical problems associated with surface micromachining?
There are major problems of mechanical nature that result from surface micro machining. These are, 1. Adhesion of layer 2. Interfacial stresses and 3. Stiction 8. What is meant by stiction.
Many have experienced the difficulty in separating two transparencies after the thin dividing paper is pulled out a similar phenomenon occurs in surface micromachining. This phenomenon of two separated pieces sticking together is called sticking. 9. What are the drawbacks in micromachining process?
Bulk and surface micromachining techniques are overshadowed by two major drawbacks. 1. The low geometric aspect ratio Geometric aspect ratio of a microstructure is the ratio of the dimension in the depth to that of the surface. Most silicon based MEMS and Microsystems use wafers of standard sizes and thickness as substrates, on which etching or thin film deposition takes place to form the desired three dimensional geometry. Severe limitation s of the depth dimension is thus unavoidable. 2. The use of silicon based materials. The other limitation is on the materials, silicon based MEMS preclude the use of conventional materials such as polymers and plastics, as well as metals for the structures and thin films
10. What are the basic requirements for photo resist material for the LIGA process?
Basic requirements for the photo resist material for the LIGA process include the following: 1. It must be sensitive to x-ray radiation 2. It must have high resolution as well as high resistance to dry and wet etching 3. It must have thermal stability up to 140°C 4. The unexposed resist must be absolutely insoluble during development. 5. It must exhibit very good adhesion to the substrate during electroplating.
11. List out the advantages of LIGA process?
1. Virtually unlimited aspect ratio of the microstructure geometry 2. Flexible microstructure configurations and geometry 3. The only one of the three techniques that allows the production of metallic microstructure. 4. The best of the three manufacturing process for mass production, with the provision for injection molding. 12. List out the Applications of semiconductor in micromachining field?
1. Microdiodes 2. Microresistors 3. Microtransistors 4. Micro LED’s 5. Single electron transistors. All these have the advantage of ballistic transport which is useful in the semiconductor industry. 13. List out the Applications of Optoelectronics in micromachining field?
1. Micromirrors 2. Adaptive optics 3. Optical switches for alignment 4. Biophotonics 5.3D printing 14. List out the Applications of Mems/Nems devices in micromachining field?
1. Mechanical sensors 2. Microfluidics 3. Acoustic mems 4. Fuel cells
15. List out the Applications of Nanostructures in micromachining field?
1. Nano wires 2. Nano sheets 3. Nano rods 4. Carbon nano tubes 15. List out the Applications of Biological systems in micromachining field?
1. Biomedical Transducers 2. Medical implants 3. Microsurgical Tools 4. Mems pressure sensors-Blood pressure 5. Micro fluidics for drug delivery. 6. Micromachined needles.
8 MARKS / 16 MARKS 11. Describe about Bulk micromachining technique? 12. Describe about Surface micromachining technique? 13. Differentiate between bulk micromachining and surface micromachining? 14. Briefly explain the LIGA process? 15. Compare wet and dry etching with suitable example? 16. Write in detail about micromachining process applications to the following fields? A) Application to semiconductor electronic devices B) Optoelectronic devices C) Mems/Nems devices
17. Write in detail about micromachining process applications to the following fields? A) Nanostructures B) Biological systems
SRI KRISHNA COLLEGE OF ENGINEERING & TECHNOLOGY KUNIAMUTHUR, COIMBATORE. DEPARTMENT OF MECHATRONICS ENGINEERING CLASS : IV MCT A and B SUBJECT : MEMS and NEMS STAFF NAME : Unit — III MEMS DEVICE PHYSICS AND DESIGN 2 mark Questions & Answers 1. Draw the block diagram for MEMS as a Micro sensor.
2. List any 4 types of micro sensors.
Acoustic Wave Sensors
Piezoelectric Sensors Thermal Sensors
Capacitive Sensors
Pressure Sensors
3 . Draw the block diagram for MEMS as a Micro actuator.
4. List the different types of actuating Techniques. Using Thermal Force
Using Piezoelectric materials Using Shape Memory Alloy Using Electrostatic Force 5. What is a Shape Memory Alloy? Give Example. SMA is the materials that have a "memory" of their original geometry (shape) at a typically elevated temperature of production. Eg: NiTinol.
6. Draw a CMOS inverter.
7. Draw CMOS NAND gate with truth table
8. Write few lines about design rules. Interface b/w designer and process engineer Permissible Geometries/Constraints on layout i. Width Rule, Space Rule, Overlap Rule Two types of layout constraints a. Resolution constraints b. Alignment / overlap constraints
9. Classify the characterization techniques used in MEMS. Scanning Probe Microscopy (SPM)
a. Scanning Tunneling Microscopy (STM) b. Atomic Force Microscopy (AFM) Electron Microscopy a. Scanning Electron Microscopy (SEM) b. Transmission Electron Microscopy (TEM) 10. What are the important requirements in SPM techniques. Accurate control of position of tip( upto 0.1 A°) Piezoelectric positioning
Sharp tip — ideally terminating in a single atom Vibration Isolation Tip Preparation
11. What are the two modes of Atomic Force Microscopy? Contact mode - short-range interactions (A) — inter atomic forces Two ways - 'constant force' feedback system moves tip in z direction to keep force constant 'constant height'no feedback system usually used when surface roughness small higher scan speeds possible
Tapping mode - long-range forces - van der Waals, electrostatic, magnetic Tip vibrates (105 Hz) close to specimen surface (50-150 A) with amplitude 10-100 nm May at times lightly contact surface 12. What can we study in a SEM? Topography and morphology
Chemistry Crystallography Orientation of grains In-situ experiments: Reactions with atmosphere Effects of temperature
13. What is Diffraction? Define its purpose in TEM. Diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit.
The diffraction mode in TEM is used to fine the elemental composition of the sample to be studied by analyzing the spot pattern or ring pattern.
14. Distinguish between TEM and SEM. TEM:
Transmission Electron Microscopy It gives the 2D image of surface High Magnification
SEM:
Scanning Electron Microscope It gives 3D image of the sample to study surface morphology. Less magnification compared to TEM
15. Draw the specimen interaction diagram when imaging is done using SEM.
16 marks
1. Describe in detail about the two types of Scanning Probe Microscopes. 2. Explain in detail about TEM and SEM 3. Describe in detail about MEMS sensors 4. Describe in detail about MEMS actuators. 5. Explain the Actuating Techniques used in MEMS. Describe any one actuator in detail.
SRI KRISHNA COLLEGE OF ENGINEERING & TECHNOLOGY KUNIAMUTHUR, COIMBATORE. DEPARTMENT OF MECHATRONICS ENGINEERING CLASS : IV MCT A and B SUBJECT : MEMS and NEMS STAFF NAME : Unit — IV INTERFACIAL PHENOMENA 2 mark questions 1. Define Surface Tension.
Force / unit length to counterbalance inward pull or tension in the surface Surface tension is typically measured in dynes/cm, the force in dynes required to break a film of length 1 cm. 2. Define Density. How is it different from viscosity. Density = mass/ volume. It totally depends on size and mass of molecules in sample. Viscosity is resistance to fluid flow. Density of oil is less than water whereas viscosity of oil is more than water.
3. Define interface Boundary between two phases Properties of molecules differ at the boundary Types of interface — dep on S, L , G Flat or Curved — dep on Surface Tension
4. Write few lines about interfacial tension Cohesive forces b/w adjacent molecules Strong bonding at the surface Surface mol exp inward pull. To keep the equilibrium, an equal force applied to opposite the inward tension
5. What is interfacial hydrodynamics?
Deals with movement of fluids and the forces acting on solid bodies immersed in fluids and in motion relative to them Deals with dynamics of fluid esp incompressible fluids
6.
Drag and define Surfactant.
Surface active agents hydrophobic Tail & Hydrophilic head A surfactant molecule is depicted schematically as a cylinder representing the hydrocarbon (hydrophobic) portion with a sphere representing the polar (hydrophilic) group attached at one end.
The hydrocarbon chains are straight because rotation around carbon-carbon bonds bends, oi ls and twists them. 7. List the different surface active agents Wetting agents Solubilizing agents
Emulsifying agents
Dispersing, Suspending and Defloculating agents
Foaming and antifoaming agents Detergents
8. What is wetting agent?
Wetting agent is a surfactant that when dissolved in water, lower the contact angle and aids in displacing the air phase at the surface and replacing it with a liquid phase. 9. Classify wettability.
When the forces of adhesion are greater than the forces of cohesion, the liquid tends to wet the surface and vice versa. Place a drop of a liquid on a smooth surface of a solid. According to the wettability, the drop will make a certain angle of contact with the solid. A contact angle is lower than 90°, the solid is called wettable • A contact angle is wider than 90°, the solid is named non -wettable. • A contact angle equal to zero indicates complete wettability.
10. What is emulsion? What are the different types of emulsions?
It is a mixture of one liquid in another immiscible liquid Types: OIW — Oil in Water WIO — Water in Oil
16 marks
1. Explain the term surface tension and its effect on interface and inside the liquid. 2. Describe in detail about the different types of wetting and its application in MEMS. 3. Give a detailed description on the term surfactants with more facts on Emulsions and foams. 4. Explain in detail about interfacial phenomena.
SRI KRISHNA COLLEGE OF ENGINEERING & TECHNOLOGY KUNIAMUTHUR, COIMBATORE. DEPARTMENT OF MECHATRONICS ENGINEERING CLASS : IV MCT A and B SUBJECT : MEMS and NEMS STAFF NAME :
Unit — V APPLICATIONS OF MEMS / NEMS 2 mark questions
1 . List the applications of MEMS pressure sensors in automotive industry to monitor and transmit
Tyre pressure Fuel Pressure Oil Pressure Air bag deployment
2. List applications of MEMS pressure sensors in Biomedical field Blood Pressure sensors Intracranial Pressure Sensors Intra Ocular Pressure Sensors
3. Write few lines about MEMS inertial Sensors Newton 's Law of inertia — An object does not tend to change its state of rest or motion unless acted upon by an external unbalanced force.
MEMS Inertial Sensors — Measures inertia — convert to measurable signal Measure changes in acceleration, vibration, orientation, inclination Accelerometers & Gyroscopes
4. List few MEMS actuators. Digital Micromirror Device Grating Light Valve Microgrippers MEMS Nozzles & Pumps
5. What is the need of signal processing? Give an example.
To amplify or modulate and convert according to the end requirement Digital signal processing (DSPs) take real-world signals like voice, audio, video, temperature, pressure or position that have been digitized and then automatically manipulate them. A DSP is designed for performing mathematical functions like "add", 'subtract", "multiply" and "divide" very quickly.
6. Distinguish between spatial and temporal resolution.
It is the measure of how closely lines can be resolved in an image is called spatial resolution, 10d it depends on properties of the system creating the image, not just the pixel resolution pixels per inch (ppi). Fix practical purposes the clarity of the image is decided by its spatial resolution, not the nurnber of pixels in an image. In effect, spatial resolution refers to the number of independent pixel values per unit length.
7. Draw the block diagram of a data acquisition system.
8. What are the types of uncertainities? Random Uncertainties: result from the randomness of measuring instruments. They can deal with by making repeated measurements and averaging. One can calculate the standard deviation of the data to estimate the uncertainty. Systematic Uncertainties: result from a flaw or limitation in the instrument or measurement technique. Systematic uncertainties will always have the same sign. For example, if a meter stick is too short, it will always produce results that are too long. 16 Marks
1. Describe in detail about the different applications of MEMS sensors. 2. Explain in detail about DAQ and signal processing. 3. What is error? How is it different from uncertainty? Explain ab out error propagation. 4. Describe in detail about the different applications of MEMS actuators.
