Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 3M

• Resistance values for conductors at any temperature other than the standard temperature on a specific resistance must be determined by the formula

  R= Rref[1+α(T-Tref]

  Where,

  R= conductor resistance at temperature T

  Rref= conductor resistance at reference temperature Tref

  .α= temperature coefficient of resistance TCR for conductor material

  T= Conductor temperature in degrees

  Tref= reference temperature that is specified for conductor material

• The TCR symbolizes the resistance change factor per degree of temperature change
• All materials have specific resistance and changes according to the temperature
• For pure metal the TCR is positive, ie the resistance increases with increase in temperature
• decreases with increase in temperature
• For alloys the TCR is zero ie the resistance hardly changes at all with variation in temperature.
• In any material the internal resistance will change as the temperature changes.
• The rate of resistance change is based on temperature and is referred to as TCR.
• It is denoted in units of Ppm/C and determined from the resistance changed from some reference temperature and change in temperature
• One advantage of poly Si over Cryst. Si is its reduced TCR
• The TCR for Poly Si and crystal is approx 0.04%/degree C. compare to 0.14%/degree C for Cryst. Si.
• The deposition process and type of dopant can alter the sign of TCR
• Emitter type Poly si have a TCR of -0.045%/degree C
• Resistance with positive TCR are used in compensating the –ve temp dependence of piezoresistance sensor.