Silicon Carbide Temperature Sensor for Harsh Environments

Team Members ADVISOR Chris Rice Jason Wallace Dr. Stephen Saddow “a hot project…a cool advisor” Michael Jackson Jovan Bjelobrk

Team Responsibilities Chris Rice Sensor Fabrication Sensor Testing Jason Wallace Documentation Device Controller PIC Coding Software Interface Device Controller PIC Coding Michael Jackson Sensor Fabrication Sensor Testing Jovan Bjelobrk

Overview No reliable way to detect temperature changes in extreme environments using typical semiconductor material (Si) Space travel involves extreme temperatures SiC has the ability to operate in and withstand extreme temperatures (>500 °C)

Key Specifications Increased Sensing Range 25 ° C to 500 ° C Tolerance Temperature reading accuracy of 0.5 °C at 25 °C Cost Cost of working unit will be less than $300

Timeline

System Components Controller Circuit Software Interface Temp. Sensor

PCB LAYOUT

User Interface

Design Equations R =  (L/A)  = 1/(qnn) Ni = sqrt(Nc*Nv)*exp(-Eg/2kT) n = (2.5*107)*T-2 A = W*t

Resistance vs. Temperature L (mm) =100 50 20 10 Test Spec of 25 to 500 degrees C

Measured Resistance V. Temperature SiC

SiC Sample

Micropipes Today, the density of micropipe defects in standard SiC commercial wafers, which are being used as substrates for SiC device fabrication, exceeds 100 cm-2. These micropipes, originated from SiC substrates, penetrate in device structures during epitaxial growth and cause the device failure "Silicon Carbide Epitaxial Wafers",http://www.tdii.com/sic-g.htm,Copyright 1997, 1998 by TDI, Inc

Sensor Cross-Section n+ n+ n- I p+

Resistance Model  = 1/(qnn) R =  (L/A)  = 1/(qpp) R(n-): -- donor carriers fully ionized -- electron mobility controls R(n-) R(n-)  = 1/(qnn) R(p+) R(p+): -- acceptor carriers are NOT fully ionized -- hole mobility is dominated by the hole ionization R =  (L/A)  = 1/(qpp)

Fractional Ionization Pd = 1E18 [cm-3] p = 10%(Pd) = 1E17 [cm-3] p >> n R(p+) << R(n-)

Calculations Re-worked Simulated Results, These are being generated!!!

Cost Analysis ~ $2000 per substrate (2 inch diameter wafer) ~ $600 for whole-wafer EPI Growth ~ $400 for Fabrication Run Producing 24 cells per wafer, and assuming overall yield of process of 72%, produces 120 usable devices at approximately $25 each Control board components: $26.61 Total cost for working unit: $51.61

Silicon Carbide Temperature Sensor for Harsh Environments