1. Measurements of Piezoresistive Coefficients in Lightly Doped (111) Silicon Chun Hyung Cho & John Sunwoo Electrical & Computer Engineering Auburn University

2. OUTLINE Introduction Piezoresistive Theory Results of Measurements Discussion Conclusion

3. INTRODUCTION Stress due to mechanical loadings Degradation of performance Stress analyses of electronic packages and their components have been performed

4. INTRODUCTION(continued) The basic application concepts Semiconductor chips are incorporated into electronic packages The sensors have most often been resistors

5. Schematic of normal 4PB fixture

6. 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

7. (111) silicon wafer & stress- induced resistance changes

8. Result: p-type resistance change Typical vaule: B 1 p =507/TPa, B 2 p = -145/TPa

9. Result: n-type resistance change Typical vaule: B 1 n =-230/TPa, B 2 n = 207/TPa

10. Discussion: Typical piezo-resistive coefficient values for BMW2

11. 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

12. 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.

13. 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.