measurements of piezoresistive coefficients in lightly doped (111) silicon chun hyung cho & john...
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Measurements of Piezoresistive Coefficients in Lightly Doped (111) Silicon
Chun Hyung Cho & John Sunwoo
Electrical & Computer Engineering
Auburn University
OUTLINE Introduction
Piezoresistive Theory
Results of Measurements
Discussion
Conclusion
INTRODUCTION Stress due to mechanical loadings
Degradation of performance
Stress analyses of electronic packages and their components have been performed
INTRODUCTION(continued)
The basic application concepts
Semiconductor chips are incorporated into electronic packages
The sensors have most often been resistors
Schematic of normal 4PB fixture
Basic BMW2 Test Chip (200 x 200 mils)
The doped active region
is typically designed
using a serpentine
pattern
Electrical isolation
between the doped
surface resistor and the
bulk of the chip
(111) silicon wafer & stress-induced resistance changes
Result: p-type resistance changeTypical vaule: B1
p =507/TPa, B2p = -145/TPa
R0/R0 vs. Stress: P-type (111 Silicon)
y = 4.588E-04x + 1.514E-04
R2 = 9.998E-01
0.000E+00
5.000E-03
1.000E-02
1.500E-02
2.000E-02
2.500E-02
3.000E-02
0 10 20 30 40 50 60 70
Uniaxial Stress (:Mpa)
R/R
R90/R90 vs. Stress: P-type (111 Silicon)
y = -1.249E-04x + 1.453E-04
R2 = 9.986E-01
-1.2000E-02
-1.0000E-02
-8.0000E-03
-6.0000E-03
-4.0000E-03
-2.0000E-03
0.0000E+00
2.0000E-03
0 20 40 60 80 100
Uniaxial Stress (:Mpa)
R/
R
Result: n-type resistance changeTypical vaule: B1
n =-230/TPa, B2n =
207/TPa
R0/R0 vs. Stress: n-type (111 Silicon)
y = -2.031E-04x
R2 = 9.880E-01
-1.400E-02
-1.200E-02
-1.000E-02
-8.000E-03
-6.000E-03
-4.000E-03
-2.000E-03
0.000E+00
0 10 20 30 40 50 60 70
Uniaxial Stress (:Mpa)
R/R
R90/R90 vs. Stress: n-type (111 Silicon)
y = 1.967E-04x
R2 = 9.967E-01
-2.0000E-03
0.0000E+00
2.0000E-03
4.0000E-03
6.0000E-03
8.0000E-03
1.0000E-02
1.2000E-02
1.4000E-02
0 10 20 30 40 50 60 70
Uniaxial Stress ( :Mpa)
R/
R
Discussion: Typical piezo-resistive coefficient values for BMW2
Typical Piezoresistive Coefficient Values For BMW-2
Test Chips (TPa)-1
Piezoresistive p-type n-type
Coefficient Silicon Silicon
507 -230
-145 207
[From J . C. Suhling, R. W. J ohnson, and R. C. J aeger]
B1
B2
DISCUSSION IntelliSuite software is used Under-estimated result Measured resistance changes was
assumed to be independent of T Beam rotation error Loading symmetry error Weight and length measurement
error
CONCLUSION Measurements of piezoresistive
coefficients in lightly doped (111) silicon Applications of piezoresistive sensors in
electronic packaging. The sensors are not mounted on the chips. Integral part of the structure to be
analyzed by the way of the fabrication process.
CONCLUSION (Continued)
The sensor are capable of providing non-intrusive measurements of surface on chip even within encapsulated packages.
Piezoresistive stress sensors have much higher sensitivity than metallic stress sensors.
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