(SEM VII) THEORY EXAMINATION 2024-25 MICRO & SMART SYSTEMS

MICRO & SMART SYSTEMS (KEC077) – COMPLETE SOLVED PAPER

Time: 3 Hours  Max Marks: 100
Instructions: Attempt all Sections

SECTION A (2 × 10 = 20 Marks)

Attempt all questions in brief

a) Any two applications of Microsystems

Biomedical devices (lab-on-chip, biosensors)

Automotive sensors (airbag accelerometers, pressure sensors)

b) Conductometric gas sensors
Sensors whose electrical conductivity changes in the presence of target gases (e.g., metal oxide gas sensors).

c) Micromachining technologies
Bulk micromachining, Surface micromachining, LIGA, DRIE.

d) Electrostatic (definition)
Concerned with forces and fields due to electric charges at rest; widely used for MEMS actuation.

e) Scaling effects in Microsystems (brief)
As size reduces, surface forces dominate over volume forces, affecting stiffness, electrostatics, heat transfer.

f) Micro and nanofabrication
Processes used to fabricate structures in the micrometer and nanometer scale using lithography, deposition, etching.

g) Types of microsensors
Mechanical, Thermal, Chemical, Optical, Magnetic, Biosensors.

h) Lithography (brief)
Pattern transfer process using light/beam exposure to define microstructures on substrates.

i) Pull-in voltage
Minimum voltage at which an electrostatically actuated MEMS structure collapses onto the electrode.

j) Diffusion
Movement of dopant atoms in a semiconductor due to concentration gradient and temperature.

SECTION B (10 × 3 = 30 Marks)

Attempt any three

a) Smart materials & Integrated Microsystems

Smart materials: Respond to external stimuli (piezoelectric, shape memory alloys).
Integrated Microsystems: Combine sensors, actuators, electronics, and control on a single platform.

b) Silicon capacitive accelerometer & piezoresistive pressure sensor

Capacitive accelerometer: Measures acceleration via change in capacitance between fixed and movable electrodes.

Piezoresistive pressure sensor: Uses resistance change in silicon strain gauges due to applied pressure.

c) Thin film deposition & Etching

Deposition: CVD, PVD for forming thin layers.

Etching: Wet and dry etching to remove material selectively.

d) Anticlastic curvature & torsion of beams

Anticlastic curvature: Opposite curvature induced in perpendicular direction during bending.

Torsion: Twisting of beams due to applied torque.

e) Integrated Microsystems & Packaging

Integrated Microsystems combine multiple functions on one chip.
Packaging steps: Die attach → Wire bonding → Encapsulation → Testing → Integration.

SECTION C (10 × 5 = 50 Marks)

Attempt one from each question

Q3(a) Miniaturization process & need

Process: Scaling down components using microfabrication techniques.
Need:                                                                 Reduced size & power

Higher performance                                           Lower cost

System integration

Q3(b) Microsystems vs MEMS

Q4(a) Portable blood analyzer & piezoelectric inkjet print head

Blood analyzer: Microfluidic system for rapid diagnostics.

Inkjet print head: Uses piezoelectric actuation to eject ink droplets precisely.

Q4(b) Micro-mirror array for video projection

Uses thousands of tilting micro-mirrors to modulate light digitally (DLP technology) for high-resolution projection.

Q5(a) Silicon micromachining & specialized materials

Silicon micromachining: Bulk and surface techniques to shape silicon.
Materials: Polysilicon, Silicon nitride, Piezoelectric materials, Polymers.

Q5(b) Advanced microfabrication processes

Deep Reactive Ion Etching (DRIE)

LIGA

Nanoimprint lithography

Atomic Layer Deposition (ALD)

Q6(a) Short notes

Bimorph effect: Bending due to different thermal expansion in layered materials.

Residual stress: Stress locked in films after fabrication.

Poisson’s effect: Lateral strain due to axial stress.

Q6(b) Coupled electro-mechanics & squeezed film effects

Coupled electro-mechanics studies interaction of electrical and mechanical domains.
Squeezed film effect: Damping caused by trapped air between moving MEMS structures.

Q7(a) Scaling effects in electrostatic & magnetic domains

Electrostatic forces: Scale favorably with miniaturization.

Magnetic forces: Weaken significantly at microscale.

Q7(b) Smart-structure vibration control (case study)

Smart structures use sensors + actuators + control algorithms (e.g., piezoelectric patches) to actively suppress vibrations in aerospace and civil structures.