Materials of Flexible & Stretchable BioMEMS

Comprehensive vocabulary flashcards covering the materials, properties, and fabrication techniques for flexible and stretchable BioMEMS as discussed in the lecture.

Conductor

A material characterized by high conductivity, low resistivity, and a completely filled conduction band with no band gap, allowing for the flow of free electrons.

Semiconductor

A material with moderate conductivity and a small band gap where current flows through both electrons and holes; its resistance decreases with an increase in temperature or the addition of doping.

Insulator

A material with almost negligible conductivity and a large band gap, typically featuring ionic bonds and a completely filled valence band.

Positive Temperature Coefficient of Resistance

A property of conductors where electrical resistance increases as the temperature increases.

Galinstan

A liquid metal alloy composed of Gallium, Indium, and Tin ($Sn$).

EGaIn

A liquid metal alloy composed of $75.2\,\%$ Gallium and $24.8\,\%$ Indium.

Percolation Threshold ($V_c$)

The critical volume fraction and minimum concentration of conducting filler required to form an interconnected, continuous, macroscopic network throughout an insulating matrix.

Soft Conductive Nanocomposite

An electrode material composed of a percolated network of nanomaterials (0D, 1D, or 2D fillers) inside an elastomer like PDMS or Ecoflex.

Tunnelling Resistance

The resistance encountered between fillers in a nanocomposite during incomplete physical contact, which increases exponentially with the interfiller distance ($D_{IP}$).

Ion Implantation

A fabrication method where metal cations are generated by plasma and accelerated to $0.2$-$10\,eV$ to create a conduction path close to the elastomer surface.

PEDOT:PSS

A key conductive polymer (poly(styrenesulfonate)) cast from water suspension that often requires conductivity enhancers and plasticizers for stability and flexibility.

Polyimide (PI)

A flexible substrate with a high glass transition temperature ($T_g = 325\,^{\circ}C$), thermal stability up to $400\,^{\circ}C$, and a low dielectric constant of $3.4$.

Parylene C

A completely linear, high crystalline polymer modified with a chlorine atom substitution, known for low moisture permeability and biocompatibility.

Parylene HT

A variant of parylene that replaces alpha hydrogen atoms with fluorine, offering high temperature resistance and long-term UV stability.

Polymethyl Methacrylate (PMMA)

A transparent, lightweight substrate with a Young's modulus of $3.3\,GPa$ and a density of $1.17\,g/cm^3$.

Polydimethylsiloxane (PDMS)

A biocompatible elastomer with a Young's modulus between $1$-$100\,MPa$ and a stretchability of up to $1000\,\%$, though it is inherently hydrophobic.

Polyurethane (PU)

A soft, flexible substrate with stretchability up to hundreds of percent, known for self-healing properties and better mechanical degradation resistance than silicone.

Laser-Induced Graphene (LIG)

A porous, conductive carbon material formed through photothermal pyrolysis via laser irradiation on organic coatings or elastomers.

Intrinsically Conducting Polymers (ICPs)

Organic materials with highly conjugated backbones (alternating single and double bonds) that achieve high conductivity through doping to introduce charge carriers like polarons.

A-174

A silane-based adhesion promoter used to improve the bonding of parylene during the patterning process.

Imidization

The chemical process Polyimide undergoes during curing (at $300$-$500\,^{\circ}C$) which typically results in material shrinkage.