ECE 875: Electronic Devices Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University

VM Ayres, ECE875, S14 Lecture 41, 21 Apr 14 Chp 14: Sensors Chemical ion sensors Temperature sensors Mechanical sensors

VM Ayres, ECE875, S14 What has changed from a conventional MOSFET: Gate Insulator Channel Substrate

VM Ayres, ECE875, S14 How to incorporate the changes: examine conventional MOSFET: Below velocity saturation =  ms : missing Q f /C ox

VM Ayres, ECE875, S14 Conventional MOSFET: =  ms : missing Q f /Cox

How to incorporate the changes: replacing metal gate with ion-rich solution:

VM Ayres, ECE875, S14 _ _ _ Dipole layer on solution side “talks” to semiconductor at its insulator surface Dominated by effect of dipole layer  missing Q f /C ox

VM Ayres, ECE875, S14 Work function difference change:

Main question is: ? Hidden question is: ?

Main question is: find I Dsat Hidden question is: find V T <= find V FB

VM Ayres, ECE875, S14 Lecture 41, 21 Apr 14 Chp 14: Sensors Chemical ion sensors Temperature sensors Mechanical sensors

Concentrations of carriers are temperature dependent: Chp. 01

Goal: use temperature effects within a device for readout: Choices:pn junction MOSFET

Goal: use temperature effects within a device for readout: Choices:pn junction MOSFET What can change as a function of temperature?

n i is related to the energy bandgap and energy bandgaps are temperature dependent Chp. 01

Goal: use temperature effects within a device for readout: Choices:pn junction MOSFET

Chp.01 Simplify the mathematics:  2 = small:

This is I as a readout as as function of V = V ext : an I-V graph with a “camouflaged” temperature dependance

Use voltage readout for better sensitivity:

In HW09: Pr. 01: