22.2 Fabrication techniques for micro-scale devices

Micro-scale devices are revolutionizing energy harvesting. Fabrication techniques like lithography, etching, and thin-film deposition enable the creation of tiny, efficient harvesters. These methods allow for precise control over device structure and properties, crucial for maximizing energy output.

Understanding these fabrication processes is key to developing cutting-edge micro-scale energy harvesters. From photolithography to wafer bonding, each technique plays a vital role in creating devices that can capture and convert small amounts of ambient energy into usable power.

Lithography and Etching

Photolithography Process and Applications

Top images from around the web for Photolithography Process and Applications

• 

  Progress in piezo-phototronic effect enhanced photodetectors - Journal of Materials Chemistry C ... View original

  Is this image relevant?

• 

  Piezoelectric energy harvesting from a PMN–PT single nanowire - RSC Advances (RSC Publishing ... View original

  Is this image relevant?

• 

  Piezoelectric energy harvesting from a PMN–PT single nanowire - RSC Advances (RSC Publishing ... View original

  Is this image relevant?

• 

  Progress in piezo-phototronic effect enhanced photodetectors - Journal of Materials Chemistry C ... View original

  Is this image relevant?

• 

  Piezoelectric energy harvesting from a PMN–PT single nanowire - RSC Advances (RSC Publishing ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Photolithography Process and Applications

• 

  Progress in piezo-phototronic effect enhanced photodetectors - Journal of Materials Chemistry C ... View original

  Is this image relevant?

• 

  Piezoelectric energy harvesting from a PMN–PT single nanowire - RSC Advances (RSC Publishing ... View original

  Is this image relevant?

• 

  Piezoelectric energy harvesting from a PMN–PT single nanowire - RSC Advances (RSC Publishing ... View original

  Is this image relevant?

• 

  Progress in piezo-phototronic effect enhanced photodetectors - Journal of Materials Chemistry C ... View original

  Is this image relevant?

• 

  Piezoelectric energy harvesting from a PMN–PT single nanowire - RSC Advances (RSC Publishing ... View original

  Is this image relevant?

1 of 3

• Photolithography transfers patterns onto substrates using light-sensitive materials
• Process involves coating substrate with photoresist, exposing to UV light through a mask, and developing the pattern
• Positive photoresists become soluble when exposed to light, while negative photoresists become insoluble
• Resolution depends on wavelength of light used (shorter wavelengths achieve finer features)
• Applications include fabricating integrated circuits, MEMS devices, and microfluidic channels

Etching Techniques and Mask Design

• Wet etching uses liquid chemicals to remove material isotropically or anisotropically
  • Isotropic etching removes material equally in all directions
  • Anisotropic etching removes material at different rates in different crystallographic directions
• Dry etching employs plasma or reactive ions to remove material with high directionality
  • Reactive Ion Etching (RIE) combines physical and chemical etching mechanisms
  • Deep Reactive Ion Etching (DRIE) achieves high aspect ratio structures
• Mask design crucial for defining patterns to be etched
  • Considers etch selectivity, undercut, and feature sizes
  • Computer-aided design (CAD) software used to create complex mask layouts

Surface and Bulk Micromachining

• Surface micromachining builds structures on top of a substrate
  • Involves depositing and patterning thin films of structural and sacrificial layers
  • Sacrificial layers removed to release movable structures (cantilevers, membranes)
• Bulk micromachining creates 3D structures by selectively removing substrate material
  • Utilizes anisotropic wet etching or deep reactive ion etching
  • Creates features like cavities, channels, and through-wafer holes
• Combination of surface and bulk micromachining enables complex MEMS devices (accelerometers, pressure sensors)

Thin-Film Deposition Techniques

Physical Vapor Deposition Methods

• Thin-film deposition creates layers ranging from nanometers to micrometers thick
• Evaporation heats source material to vaporization point in vacuum
  • Thermal evaporation uses resistive heating
  • Electron beam evaporation uses focused electron beam for higher melting point materials
• Sputtering bombards target material with energetic ions to eject atoms
  • DC sputtering for conductive materials (metals)
  • RF sputtering for insulating materials (ceramics, polymers)
• Pulsed Laser Deposition (PLD) uses high-power laser pulses to vaporize target material

Chemical Vapor Deposition Processes

• Chemical Vapor Deposition (CVD) forms solid films through chemical reactions of gaseous precursors
• Thermal CVD relies on heat to activate chemical reactions
  • Low Pressure CVD (LPCVD) operates at reduced pressures for improved uniformity
  • Atmospheric Pressure CVD (APCVD) offers higher deposition rates
• Plasma-Enhanced CVD (PECVD) uses plasma to enhance chemical reactions
  • Allows lower deposition temperatures suitable for temperature-sensitive substrates
• Atomic Layer Deposition (ALD) deposits films one atomic layer at a time
  • Achieves precise thickness control and excellent conformality

Microfabrication Processes

Advanced Micromachining Techniques

• Micromachining creates 3D microstructures and devices
• Laser micromachining uses focused laser beams to ablate or modify materials
  • Enables precise cutting, drilling, and surface texturing
• Focused Ion Beam (FIB) micromachining uses accelerated ions for milling and deposition
  • Allows maskless, direct-write patterning and circuit editing
• Electrochemical micromachining removes material through controlled electrochemical dissolution
  • Suitable for conductive materials and creating high aspect ratio structures

Wafer Bonding and Packaging

• Wafer bonding joins two or more wafers to form a single substrate
• Direct bonding (fusion bonding) joins wafers through intermolecular forces
  • Requires ultra-clean, smooth surfaces and high-temperature annealing
• Anodic bonding joins silicon to glass using electrostatic forces and heat
• Eutectic bonding uses metal alloys that form a eutectic mixture at the bonding interface
• Packaging protects devices from environmental factors and provides electrical connections
  • Includes die attachment, wire bonding, and encapsulation

Clean Room Protocols and Contamination Control

• Clean rooms maintain controlled environments with low particle counts
• Clean room classifications based on maximum allowed particles per cubic foot of air
  • Class 100 (ISO 5) allows maximum 100 particles (≥0.5 μm) per cubic foot
• Gowning procedures prevent contamination from personnel
  • Includes cleanroom suits, gloves, boots, and face masks
• Airflow management uses laminar flow to minimize particle movement
• Equipment and material handling protocols prevent cross-contamination
• Regular monitoring and maintenance ensure clean room integrity
  • Particle counters, air samplers, and surface cleanliness tests