8.2 Fabrication techniques and assembly methods

Piezoelectric stack actuators are complex devices that require specialized manufacturing techniques. This section dives into the nitty-gritty of how these actuators are made, from creating thin ceramic layers to applying electrodes and assembling the final product.

The fabrication process involves precise methods like tape casting and screen printing, while assembly relies on thermal bonding and careful electrical connections. Post-processing, especially poling, is crucial for maximizing the actuator's performance in real-world applications.

Fabrication Techniques

Ceramic Layer Formation

Top images from around the web for Ceramic Layer Formation

• 

  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?

• 

  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?

• 

  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 Ceramic Layer Formation

• 

  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?

• 

  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?

• 

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

  Is this image relevant?

1 of 3

• Tape casting creates thin, uniform ceramic sheets by spreading slurry onto a moving carrier film
  • Slurry consists of ceramic powder, binders, and solvents
  • Controlled thickness achieved through doctor blade adjustment
  • Produces flexible green tapes ready for further processing
• Screen printing deposits patterned layers of ceramic material onto substrates
  • Uses a mesh screen with a stencil to selectively apply ceramic paste
  • Allows for precise control of layer thickness and pattern geometry
  • Commonly used for creating internal electrodes in multilayer actuators

Electrode Application and Shaping

• Electrode deposition applies conductive layers to ceramic surfaces
  • Methods include sputtering, evaporation, and electroplating
  • Thin, uniform electrode layers crucial for efficient piezoelectric performance
  • Materials used include silver, gold, and platinum
• Dicing cuts larger ceramic blocks or wafers into smaller, precisely sized elements
  • Utilizes diamond-tipped saw blades for clean, accurate cuts
  • Allows for creation of individual piezoelectric elements or arrays
  • Critical for achieving desired dimensions and tolerances in final devices

Assembly Methods

Thermal Processing and Bonding

• Co-firing simultaneously sinters ceramic layers and electrodes at high temperatures
  • Consolidates multiple layers into a dense, monolithic structure
  • Requires careful material selection to match shrinkage rates and prevent delamination
  • Temperatures typically range from 1000°C to 1300°C depending on ceramic composition
• Lamination joins multiple ceramic layers together under heat and pressure
  • Creates strong interfacial bonds between layers
  • Often used in conjunction with screen-printed internal electrodes
  • Can incorporate organic binders that burn out during subsequent firing

Electrical Connections and Protection

• Wire bonding establishes electrical connections between electrodes and external circuitry
  • Uses thin wires (gold, aluminum) to create conductive paths
  • Techniques include thermocompression, ultrasonic, and thermosonic bonding
  • Ensures reliable electrical contact for signal transmission and power delivery
• Encapsulation protects piezoelectric devices from environmental factors
  • Materials used include epoxy resins, silicone, and specialized polymers
  • Provides mechanical support and electrical insulation
  • Can incorporate features for stress relief and thermal management

Post-Processing

Electric Field Alignment

• Poling aligns dipoles within the piezoelectric material to maximize electromechanical coupling
  • Applies strong electric field (typically 2-4 kV/mm) at elevated temperatures
  • Temperature often set just below the Curie point of the material
  • Duration ranges from minutes to hours depending on material properties
  • Critical step for activating piezoelectric properties in the fabricated device
  • Can be performed on individual elements or entire assembled actuators
  • Proper poling significantly enhances piezoelectric coefficients and device performance