2026 question paper
Bio MEMS
28 questions
Q1(a). Which sequence most appropriately represents the basic microfabrication flow? (i) Etching → Lithography → Deposition (ii) Deposition → Lithography → Etching (iii) Lithography → Etching → Packaging only (iv) Packaging → Lithography → Deposition20262m
Module 3: Fabrication Techniques
View this question on its own page →Which sequence most appropriately represents the basic microfabrication flow?
(i) Etching → Lithography → Deposition
(ii) Deposition → Lithography → Etching
(iii) Lithography → Etching → Packaging only
(iv) Packaging → Lithography → DepositionWorked SolutionAnswer: (ii) Deposition → Lithography → Etching
A thin film is deposited first, lithography then defines the pattern in photoresist, and etching transfers that pattern into the film. Packaging comes last, after the device is released and tested.
Q1(b). The primary purpose of photolithography in MEMS fabrication is to: (i) Increase the thickness of a substrate (ii) Remove all deposited material (iii) Transfer a pattern onto a substrate (iv) Measure fluid pressure20262m
Module 1: MEMS Overview
View this question on its own page →The primary purpose of photolithography in MEMS fabrication is to:
(i) Increase the thickness of a substrate
(ii) Remove all deposited material
(iii) Transfer a pattern onto a substrate
(iv) Measure fluid pressureWorked SolutionAnswer: (iii) Transfer a pattern onto a substrate
Photolithography uses light to copy a mask pattern into a photosensitive resist layer. That resist then acts as a template for etching or deposition.
Q1(c). Which of the following is a major advantage of MEMS technology? (i) Large physical dimensions (ii) High power consumption (iii) Miniaturization and integration (iv) Requirement of manual operation20262m
Module 1: MEMS Overview
View this question on its own page →Which of the following is a major advantage of MEMS technology?
(i) Large physical dimensions
(ii) High power consumption
(iii) Miniaturization and integration
(iv) Requirement of manual operationWorked SolutionAnswer: (iii) Miniaturization and integration
MEMS devices are tiny, batch-fabricated and low-power, and they can be integrated with electronics on one chip, which cuts size and cost.
Q1(d). Which parameter is particularly important in determining the flow regime inside a microfluidic channel? (i) Reynolds number (ii) Atomic number (iii) Optical wavelength only (iv) Melting point20262m
Module 2: Fundamentals of Microfluidic Systems
View this question on its own page →Which parameter is particularly important in determining the flow regime inside a microfluidic channel?
(i) Reynolds number
(ii) Atomic number
(iii) Optical wavelength only
(iv) Melting pointWorked SolutionAnswer: (i) Reynolds number
Re = ρvD/μ compares inertial to viscous forces. In microchannels Re is usually far below 2000 (often below 1), so the flow is laminar.
Q1(e). Which of the following is an important consideration when selecting a polymer for BioMEMS applications? (i) Biocompatibility (ii) Color alone (iii) Maximum bulk size (iv) Magnetic behavior only20262m
Module 2: Fundamentals of Microfluidic Systems
View this question on its own page →Which of the following is an important consideration when selecting a polymer for BioMEMS applications?
(i) Biocompatibility
(ii) Color alone
(iii) Maximum bulk size
(iv) Magnetic behavior onlyWorked SolutionAnswer: (i) Biocompatibility
A BioMEMS polymer touches blood, cells or tissue, so it must not be toxic or trigger an immune response. Common examples are PDMS, PMMA and parylene.
Q1(f). In UV lithography, ultraviolet radiation is primarily used to: (i) Pattern a photosensitive material (ii) Pump fluid directly (iii) Concentrate biological cells (iv) Measure fluid pressure20262m
Module 3: Fabrication Techniques
View this question on its own page →In UV lithography, ultraviolet radiation is primarily used to:
(i) Pattern a photosensitive material
(ii) Pump fluid directly
(iii) Concentrate biological cells
(iv) Measure fluid pressureWorked SolutionAnswer: (i) Pattern a photosensitive material
UV light changes the solubility of the photoresist in the exposed regions, which defines the pattern after development.
Q1(g). A major objective of lithography in MEMS fabrication is to achieve: (i) Controlled pattern definition (ii) Fluid sterilization (iii) Cell growth only (iv) Mechanical packaging only20262m
Module 3: Fabrication Techniques
View this question on its own page →A major objective of lithography in MEMS fabrication is to achieve:
(i) Controlled pattern definition
(ii) Fluid sterilization
(iii) Cell growth only
(iv) Mechanical packaging onlyWorked SolutionAnswer: (i) Controlled pattern definition
Lithography fixes the size, shape and position of features, so later etching or deposition acts only where intended.
Q1(h). Microfluidic strategies for Lab-on-Chip systems may be used for: (i) Sample transport and processing (ii) Only external power generation (iii) Only mechanical packaging (iv) Only substrate polishing20262m
Module 4: Microfluidic Integration and Lab-on-Chip Systems
View this question on its own page →Microfluidic strategies for Lab-on-Chip systems may be used for:
(i) Sample transport and processing
(ii) Only external power generation
(iii) Only mechanical packaging
(iv) Only substrate polishingWorked SolutionAnswer: (i) Sample transport and processing
Lab-on-chip strategies move, mix, separate and react very small fluid volumes on the chip.
Q1(i). The primary function of a micropump in a microfluidic system is to: (i) Pattern the substrate (ii) Drive or transport fluid (iii) Detect biological molecules only (iv) Deposit thin films20262m
Module 5: Microfluidic Actuation Systems: Micropumps and Valves
View this question on its own page →The primary function of a micropump in a microfluidic system is to:
(i) Pattern the substrate
(ii) Drive or transport fluid
(iii) Detect biological molecules only
(iv) Deposit thin filmsWorked SolutionAnswer: (ii) Drive or transport fluid
A micropump supplies the pressure or force that moves liquid through the microchannels.
Q1(j). A microfluidic valve is primarily used to: (i) Control fluid flow (ii) Generate UV radiation (iii) Perform lithography (iv) Detect cell morphology20262m
Module 5: Microfluidic Actuation Systems: Micropumps and Valves
View this question on its own page →A microfluidic valve is primarily used to:
(i) Control fluid flow
(ii) Generate UV radiation
(iii) Perform lithography
(iv) Detect cell morphologyWorked SolutionAnswer: (i) Control fluid flow
A microvalve starts, stops, directs or meters flow in a microfluidic circuit.
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Q2(a). Explain the basic characteristics and salient features of MEMS technology.20267m
Module 1: MEMS Overview
View this question on its own page →Explain the basic characteristics and salient features of MEMS technology.
Worked SolutionMEMS: basic characteristics and salient features
Definition: MEMS (Micro-Electro-Mechanical Systems) are miniaturised devices, typically 1 µm to 1 mm in size, that combine mechanical elements, sensors, actuators and electronics on a common substrate (usually silicon) using micro-fabrication.
MermaidDiagramRendering diagram…Basic characteristics
- Microscale size: moving parts range from a few microns to a few hundred microns.
- Multi-domain: couples mechanical, electrical, thermal, fluidic and optical effects.
- Batch fabrication: many devices are made on one wafer using IC-style processes.
- Surface forces dominate: the surface-to-volume ratio is large, so stiction, surface tension and electrostatic forces matter more than gravity or inertia.
Salient features
Feature Benefit Miniaturisation Small, light, easy to embed (implants, wearables) Low power Small masses need little energy Batch production Low cost per device at high volume Integration with ICs Sensing, signal conditioning and actuation on one chip High sensitivity and fast response Low mass gives a high resonant frequency Reliability Few wearing parts; repeatable fabrication Typical materials
Silicon, silicon dioxide, silicon nitride, polysilicon, polymers (PDMS, SU-8), glass, piezoelectric films (PZT, ZnO).
Exam tip
Write the definition first, then 4 to 5 features with a one-line reason each. A block diagram earns presentation marks.
Q2(b). Discuss the historical development of MEMS technology.20267m
Module 1: MEMS Overview
View this question on its own page →Discuss the historical development of MEMS technology.
Worked SolutionHistorical development of MEMS
MEMS grew out of integrated-circuit technology: once silicon was understood as an electronic material, researchers began using it as a mechanical one too.
Period Milestone 1954 C. S. Smith reports the piezoresistive effect in silicon and germanium 1959 Richard Feynman's lecture "There's Plenty of Room at the Bottom" inspires miniaturisation 1967 H. Nathanson's resonant gate transistor, an early micromechanical device 1970s Bulk-micromachined silicon pressure sensors become commercial 1982 K. Petersen's paper "Silicon as a Mechanical Material" 1980s Surface micromachining and polysilicon microstructures; first micromotors 1990s MEMS accelerometers for automotive airbags; micromirror arrays for projection 2000s Inertial sensors in phones, RF MEMS, microfluidics and BioMEMS Today Wearables, implants, lab-on-chip and IoT sensors MermaidDiagramRendering diagram…Exam tip
Remember 3 anchor dates (1954, 1959, 1982) and one application per decade.
Q3(a). Explain the working principles of MEMS sensors and actuators with suitable examples.20267m
Module 1: MEMS Overview
View this question on its own page →Explain the working principles of MEMS sensors and actuators with suitable examples.
Worked SolutionWorking principles of MEMS sensors and actuators
MermaidDiagramRendering diagram…Sensors (physical quantity to electrical signal)
Principle How it works Example Piezoresistive Strain changes the resistance of a diffused resistor in a bridge Pressure sensor with a silicon diaphragm Capacitive Motion changes the gap or overlap, so capacitance changes Accelerometer, microphone Piezoelectric Stress generates charge Ultrasound transducer, vibration sensor Thermal Temperature changes resistance or voltage Flow sensor, thermopile Actuators (electrical signal to motion or force)
Principle How it works Example Electrostatic Attraction between charged plates, F = εAV²/(2g²) Comb-drive resonator, micromirror Thermal Joule heating causes expansion; a bimorph bends Thermal microgripper Piezoelectric Applied voltage deforms the film Micropump diaphragm, inkjet head Electromagnetic Current in a magnetic field gives a Lorentz force Micro relay, magnetic microvalve Example: capacitive accelerometer
A proof mass hangs on springs between fixed plates. Acceleration moves the mass, one capacitor gap shrinks and the other grows, and the capacitance difference gives the acceleration.
Exam tip
Give one clear row each for sensor and actuator, name the transduction principle, and add one real device.
Q3(b). Describe the principle and process of photolithography used in MEMS fabrication.20267m
Module 1: MEMS Overview
View this question on its own page →Describe the principle and process of photolithography used in MEMS fabrication.
Worked SolutionPhotolithography in MEMS fabrication
Principle: a light-sensitive polymer (photoresist) is exposed to UV light through a patterned mask. Exposure changes the resist's solubility, so after development the mask pattern remains as a resist stencil on the substrate. The stencil then protects the surface during etching or deposition.
MermaidDiagramRendering diagram…Process steps
- Cleaning: remove particles and organics, bake off moisture, add an adhesion promoter (HMDS) if needed.
- Spin coating: resist thickness is set by viscosity and spin speed.
- Soft bake: drives off solvent so the film is stable.
- Alignment and exposure: the mask is aligned to wafer marks and UV passes through its clear areas.
- Development: the developer dissolves the soluble regions.
- Hard bake: hardens the resist and improves etch resistance.
- Pattern transfer: etch the exposed film, or deposit and lift off.
- Resist strip: remove the remaining resist.
Positive and negative resist
Positive Negative Exposed area Becomes soluble Becomes insoluble (cross-links) Pattern Same as the mask Inverse of the mask Resolution Higher Lower, but thick films possible Example AZ and S1800 series SU-8 Resolution
Minimum feature size R ≈ k₁λ/NA for projection systems, so a shorter wavelength gives finer features.
Exam tip
Draw the step-by-step cross-section figure and label resist, mask, UV and substrate.
Q4(a). Explain the working principle of a microfluidic channel with a suitable schematic diagram.20267m
Module 2: Fundamentals of Microfluidic Systems
View this question on its own page →Explain the working principle of a microfluidic channel with a suitable schematic diagram.
Worked SolutionWorking principle of a microfluidic channel
A microfluidic channel is a tiny conduit, typically 10 to 500 µm wide, etched or moulded in silicon, glass or a polymer and sealed with a cover. It carries nanolitre to microlitre volumes of liquid from an inlet to an outlet.
SVGVector Architecture Diagram (SVG)Working principle
- Driving force: a syringe pump, pressure source, electric field (electroosmosis) or capillary action pushes the liquid through the channel.
- Laminar flow: the Reynolds number Re = ρvD_h/μ is small (usually well below 100 and often below 1), so streams move in parallel layers without turbulence. Mixing happens only by diffusion.
- Velocity profile: pressure-driven flow is parabolic: zero at the walls (no-slip) and maximum at the centre.
- Hydraulic resistance: flow rate Q = ΔP/R_h. For a circular channel R_h = 8μL/(πr⁴); for a rectangular channel it rises sharply as the height shrinks, so very small channels need high pressure.
- Surface effects: surface tension, capillarity and wall charge dominate at this scale.
Key relations
Quantity Expression Reynolds number Re = ρvD_h/μ Hydraulic diameter D_h = 4A/P (A = area, P = wetted perimeter) Flow rate Q = ΔP/R_h Diffusive mixing time t ≈ w²/D Exam tip
Draw the labelled side view, show the parabolic profile, and state that the flow is laminar because Re is small.
Q4(b). Discuss different types of microfluidic channels and explain their operating principles.20267m
Module 2: Fundamentals of Microfluidic Systems
View this question on its own page →Discuss different types of microfluidic channels and explain their operating principles.
Worked SolutionTypes of microfluidic channels and their operating principles
Microchannels are classified by geometry and by how the fluid is driven.
By geometry and function
Type Description Use Straight channel Simple uniform path Reaction, detection, separation Serpentine (meander) Long folded path in a small area Mixing, long residence time, PCR T- and Y-junction Two inlets merge into one outlet Laminar mixing, droplet generation Flow-focusing Sheath flows squeeze the core stream Droplet generation, cell focusing Spiral Curved path creates Dean flow Inertial cell separation Branched / tree Splits flow into parallel channels Distribution, gradient generators By driving principle
Type Operating principle Pressure-driven A pump or syringe applies ΔP; parabolic (Poiseuille) profile, Q = ΔP/R_h Electrokinetic (electroosmotic) An electric field moves the ionic layer along charged walls; nearly flat (plug) profile Capillary-driven Surface tension pulls liquid into hydrophilic channels; no external pump Centrifugal Rotation of a disc pushes fluid outward; valves set by spin speed By cross-section
Rectangular (common from soft lithography), trapezoidal or V-shaped (anisotropic KOH etching of silicon), semicircular (isotropic etching of glass), circular (capillary tubes).
MermaidDiagramRendering diagram…Exam tip
Two tables (geometry and driving force) plus the hydraulic-resistance idea give full marks.
Q5(a). Explain the basic principle of lithography.20267m
Module 3: Fabrication Techniques
View this question on its own page →Explain the basic principle of lithography.
Worked SolutionBasic principle of lithography
Lithography (Greek: lithos = stone, graphein = to write) transfers a designed pattern from a master (mask or beam) into a radiation-sensitive layer, the resist, on a substrate. The resist is then a temporary stencil for etching, deposition or doping.
MermaidDiagramRendering diagram…Working idea
Radiation (UV, electron beam, X-ray) changes the chemistry of the resist.
- Positive resist: the exposed region becomes soluble and is washed away.
- Negative resist: the exposed region cross-links and stays.
Types of lithography
Type Radiation Feature Photolithography UV light (g-line, i-line, DUV) Workhorse of MEMS; low cost Electron-beam Focused electrons Nanometre resolution; serial, slow, no mask X-ray (LIGA) Synchrotron X-rays Very tall, high-aspect-ratio structures Soft lithography Elastomer stamp (PDMS) Cheap microfluidics, replica moulding Nanoimprint Mechanical embossing High-resolution replication Key parameters
Resolution R ≈ k₁λ/NA, depth of focus, alignment accuracy, resist sensitivity and contrast.
Exam tip
Define lithography, state the positive/negative idea, then list the types in a table.
Q5(b). Explain UV lithography for SU-8. Describe the major steps involved in pattern formation.20267m
Module 3: Fabrication Techniques
View this question on its own page →Explain UV lithography for SU-8. Describe the major steps involved in pattern formation.
Worked SolutionUV lithography with SU-8: pattern formation
SU-8 is an epoxy-based, chemically amplified negative photoresist (EPON SU-8 resin with a photoacid generator in a solvent). UV exposure releases acid that triggers cross-linking during the post-exposure bake. It gives thick films and very high-aspect-ratio structures.
MermaidDiagramRendering diagram…Steps
- Substrate preparation: clean and dehydrate; an adhesion layer may be used.
- Spin coating: spin speed and SU-8 grade set the thickness (about 1 µm to several hundred µm).
- Soft bake: evaporates solvent; a slow ramp avoids cracking.
- UV exposure: near-UV (i-line, 365 nm) through a mask; thicker films need a larger dose.
- Post-exposure bake (PEB): acid in the exposed region diffuses and cross-links the epoxy.
- Development: unexposed SU-8 dissolves in a developer such as PGMEA.
- Rinse and dry: isopropanol rinse, nitrogen dry.
- Hard bake (optional): improves stability and reduces cracks.
Why SU-8 for BioMEMS
- Aspect ratios above 20:1 are achievable.
- Chemically and thermally stable once cured.
- Used as the master mould for PDMS soft lithography and for permanent channels.
Exam tip
Stress that SU-8 is negative: the exposed region stays and the unexposed region dissolves.
Q6(a). Define Micro Total Analysis System (μTAS).20267m
Module 4: Microfluidic Integration and Lab-on-Chip Systems
View this question on its own page →Define Micro Total Analysis System (μTAS).
Worked SolutionMicro Total Analysis System (μTAS)
Definition: a μTAS integrates all steps of a chemical or biological analysis (sample intake, preparation, reaction, separation and detection) on one miniature device. The concept was introduced by Manz and co-workers in 1990 and is closely related to the Lab-on-a-Chip (LoC).
MermaidDiagramRendering diagram…Advantages
- Very small sample and reagent volumes (nL to µL)
- Fast analysis and high throughput
- Portable, suitable for point-of-care use
- Automation lowers contamination and human error
- Low cost per test when mass-produced
Applications
Blood glucose and clinical diagnostics, DNA analysis (PCR-on-chip), pathogen detection, drug screening, environmental water testing, food safety.
Exam tip
The key words are "total" (all steps) and "integration on a single chip".
Q6(b). Explain the function of microfluidic valves.20267m
Module 5: Microfluidic Actuation Systems: Micropumps and Valves
View this question on its own page →Explain the function of microfluidic valves.
Worked SolutionFunction of microfluidic valves
A microvalve controls the flow of liquid or gas in a microfluidic circuit. It decides when, where and how much fluid moves.
Main functions
- Start / stop: open or close a channel.
- Direct flow: route fluid to one of several branches.
- Regulate: change flow rate or pressure.
- Isolate: seal a chamber for reaction (e.g. PCR) or incubation.
- Meter: release a precise volume.
- Prevent backflow: check valves keep flow one-directional, especially in micropumps.
MermaidDiagramRendering diagram…Classification
Class Principle Examples Active Needs external energy and control Pneumatic PDMS membrane, piezoelectric, thermopneumatic, electrostatic, electromagnetic Passive Opens and closes by fluid pressure or geometry Flap check valve, ball check valve, capillary burst valve Example: pneumatic PDMS valve
A control channel crosses a flow channel with a thin PDMS membrane between them. Pressure in the control channel bends the membrane down and pinches the flow channel shut.
Exam tip
List 4 or 5 functions, then give the active/passive table.
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Q7(a). Describe the basic design and fabrication considerations for micropumps and valves used in microfluidic systems.20267m
Module 5: Microfluidic Actuation Systems: Micropumps and Valves
View this question on its own page →Describe the basic design and fabrication considerations for micropumps and valves used in microfluidic systems.
Worked SolutionDesign and fabrication considerations for micropumps and valves
Design considerations
Factor What to decide Flow rate and pressure Target µL/min and pressure head from the application Actuation principle Piezoelectric (fast, high force), thermopneumatic (simple, slow), electrostatic (low power, small stroke), electromagnetic (large force, bulky) Chamber and diaphragm Stroke volume, compression ratio, diaphragm material and thickness Valve type Passive check valves (no power, simple) or active valves (controllable) Fluid compatibility Biocompatibility, low protein adsorption, tolerance to bubbles and particles Dead volume Keep small to avoid carry-over and trapped air Power and size Low power for portable and implantable use MermaidDiagramRendering diagram…Fabrication considerations
- Silicon bulk micromachining: KOH or DRIE etching for chambers and valve seats.
- Glass: wet etching and anodic bonding to silicon for sealed, transparent devices.
- Polymers (PDMS, PMMA): soft lithography, hot embossing or injection moulding; low cost and biocompatible.
- Actuator integration: bonding a piezoelectric disc, heater or electrodes to the diaphragm.
- Bonding and sealing: anodic, thermal, adhesive or plasma bonding without clogging channels.
- Fluidic interconnects: reliable, low-leak inlet and outlet ports.
- Packaging and sterilisation: needed for biomedical use.
Exam tip
Split the answer into design and fabrication, and give at least one material and one process for each.
Q7(b). Explain the role of BioMEMS in cell manipulation.20267m
Module 6: BioMEMS and Microscale Techniques for Biomedical Applications
View this question on its own page →Explain the role of BioMEMS in cell manipulation.
Worked SolutionRole of BioMEMS in cell manipulation
Cells are about 5 to 20 µm in size, the same scale as microchannels, so BioMEMS devices can handle single cells gently and precisely.
Functions
- Trapping and positioning: microwells, hydrodynamic traps, optical or dielectrophoretic traps.
- Sorting and separation: by size, shape, charge, magnetic label or electrical properties.
- Focusing and counting: sheath flow and inertial focusing; on-chip flow cytometry.
- Lysis and sample preparation: release DNA, RNA or proteins.
- Culture and stimulation: organ-on-chip and gradient generators.
- Single-cell analysis: read-out of one cell at a time.
MermaidDiagramRendering diagram…Techniques
Technique Force used Dielectrophoresis (DEP) Non-uniform AC field acts on polarisable cells Magnetophoresis Magnetic force on cells tagged with magnetic beads Acoustophoresis Acoustic radiation force from standing waves Optical tweezers Focused laser light traps a cell Hydrodynamic and inertial Channel geometry and flow; label-free Advantages
Tiny sample volume, high throughput, gentle handling, label-free options and integration with detection.
Exam tip
Mention at least three techniques and one application, such as circulating tumour cell isolation.
Q8(a). Discuss the role of auxiliary supporting systems, micropumps and valves in an integrated Lab-on-Chip system.20267m
Module 4: Microfluidic Integration and Lab-on-Chip Systems
View this question on its own page →Discuss the role of auxiliary supporting systems, micropumps and valves in an integrated Lab-on-Chip system.
Worked SolutionAuxiliary systems, micropumps and valves in an integrated Lab-on-Chip
A LoC works only when fluid handling, control and read-out are integrated. Micropumps and valves provide the fluid motion, and the auxiliary systems keep the chip running.
MermaidDiagramRendering diagram…Role of each part
Part Role Micropump Moves sample and reagents through channels at a controlled rate Microvalve Routes, meters, isolates and prevents backflow Mixer Speeds up mixing, which is slow by diffusion in laminar flow Heater and temperature control Needed for PCR and enzyme reactions Sensors and detectors Optical, electrochemical or electrical read-out Power and control electronics Drive pumps, valves and sensors; sequence the steps Fluidic interconnects and packaging Connect the chip to the outside and keep it sealed Data processing Converts the signal to a result for the user Why integration matters
Without on-chip pumps and valves, the chip needs bulky external equipment and loses portability. With them, a complete test can run automatically from a drop of sample.
Exam tip
Draw the block diagram and explain each block in one line.
Q8(b). Explain the principles and applications of microfabricated sample extraction and concentration techniques in BioMEMS.20267m
Module 6: BioMEMS and Microscale Techniques for Biomedical Applications
View this question on its own page →Explain the principles and applications of microfabricated sample extraction and concentration techniques in BioMEMS.
Worked SolutionMicrofabricated sample extraction and concentration in BioMEMS
Real samples (blood, saliva, water) contain the target at very low concentration among many other components. Extraction separates the target from the matrix, and concentration raises its amount per unit volume so that detection becomes possible.
Extraction techniques
Technique Principle Application Solid-phase extraction Target binds to beads, pillars or functionalised walls and is then eluted DNA and protein purification Liquid-liquid extraction Target diffuses across the laminar interface between two liquids Sample clean-up Filtration Weirs, pillar arrays or membranes block cells and particles Plasma from blood Immunomagnetic capture Antibody-coated magnetic beads are held by a magnet Pathogen and cell isolation Dielectrophoresis Field gradient traps cells or particles Cell capture Concentration techniques
- Field-amplified sample stacking and isotachophoresis: ions accumulate at a conductivity boundary.
- Ion concentration polarisation: nanochannel membranes build up charged analytes.
- Bead-based preconcentration: target collected on beads, then eluted in a small volume.
- Evaporation or membrane-based: removes solvent.
MermaidDiagramRendering diagram…Applications
DNA extraction for PCR-on-chip, isolating circulating tumour cells, pathogen detection in water and blood, and point-of-care diagnostics.
Exam tip
Give the extraction and concentration tables and a one-line principle for each.
Q9(a). Write a short note on: MEMS technology20267m
Module 1: MEMS Overview
View this question on its own page →Write a short note on: MEMS technology
Worked SolutionShort note: MEMS technology
MEMS (Micro-Electro-Mechanical Systems) technology combines micro-sized mechanical structures, sensors, actuators and electronics on one chip, made by silicon micro-fabrication.
MermaidDiagramRendering diagram…- Fabrication: bulk micromachining, surface micromachining, LIGA and soft lithography.
- Features: miniaturisation, low power, batch production, integration with ICs.
- Materials: silicon, polysilicon, silicon nitride, glass, polymers, piezoelectric films.
- Typical devices: accelerometers, pressure sensors, gyroscopes, micromirrors, microphones, microfluidic chips.
- Challenges: stiction, packaging cost, reliability and calibration.
Exam tip
One definition, one flow diagram, and one list of features and applications is enough for a short note.
Q9(b). Write a short note on: Thin-film deposition techniques20267m
Module 3: Fabrication Techniques
View this question on its own page →Write a short note on: Thin-film deposition techniques
Worked SolutionShort note: Thin-film deposition techniques
Thin films (nm to a few µm) form the structural, sacrificial, insulating and conducting layers of MEMS. Deposition methods fall into two groups.
MermaidDiagramRendering diagram…Method Principle Typical films Evaporation (PVD) Heated source vaporises in vacuum and condenses on the substrate Al, Au contacts Sputtering (PVD) Ion bombardment ejects target atoms that coat the substrate Metals, ZnO, PZT LPCVD Gas reaction at low pressure and high temperature; uniform films Polysilicon, silicon nitride PECVD Plasma allows reaction at a lower temperature Silicon oxide, nitride Thermal oxidation Silicon reacts with O₂ or steam at high temperature SiO₂ Electroplating Metal ions deposited from solution by current Thick Ni, Cu, Au (LIGA) Spin coating Liquid spread by centrifugal force, then cured Photoresist, polymers, SU-8 Selection factors
Film uniformity, step coverage, stress, deposition temperature, rate and cost.
Exam tip
Divide into PVD and CVD, then give one-line principles and examples in a table.
Q9(c). Write a short note on: MEMS applications20267m
Module 1: MEMS Overview
View this question on its own page →Write a short note on: MEMS applications
Worked SolutionShort note: MEMS applications
Field Devices Automotive Airbag accelerometers, tyre-pressure sensors, gyroscopes for stability control Consumer electronics Phone accelerometer, gyroscope, microphone, pressure sensor; inkjet print heads Medical and BioMEMS Blood-pressure sensors, lab-on-chip, drug-delivery pumps, implantable sensors, neural probes Aerospace and defence Inertial navigation, micro-gyroscopes, vibration sensing Optical Micromirror arrays for projection, optical switches Telecom RF MEMS switches, filters and resonators Industrial and IoT Flow, gas and vibration sensors, structural monitoring MermaidDiagramRendering diagram…Exam tip
Give at least five fields with one named device each.
Q9(d). Write a short note on: MEMS sensors and Actuators20267m
Module 1: MEMS Overview
View this question on its own page →Write a short note on: MEMS sensors and Actuators
Worked SolutionShort note: MEMS sensors and actuators
A sensor converts a physical quantity (pressure, acceleration, temperature, flow) into an electrical signal. An actuator converts an electrical signal into motion, force or fluid movement.
MermaidDiagramRendering diagram…Sensor Actuator Principles Piezoresistive, capacitive, piezoelectric, thermal Electrostatic, thermal, piezoelectric, electromagnetic Examples Pressure sensor, accelerometer, gyroscope Micromirror, micropump, microvalve, microgripper Output Electrical signal Mechanical or fluidic action Together they form a closed loop: the sensor measures, the controller decides, and the actuator acts.
Exam tip
Use a two-column comparison table with at least two principles and two examples each.
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