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.