This document summarizes research on using optical control to tune the frequency and turn on/off thermal-piezoresistive self-sustained oscillators. Illuminating the oscillators with a HeNe laser changes their piezoresistive coefficient by exciting charge carriers, which affects heat dissipation and temperature. Experiments showed that illumination could increase oscillator frequency by stiffening the material and decrease it by lowering temperature. The work demonstrates a new method for integrating these oscillators with photonic circuits using optical control of their piezoresistive properties.

1. OPTICAL CONTROLAND TUNING OF THERMAL-
PIEZORESISTIVE SELFSUSTAINED OSCILLATORS
Author: Harris J. Hall, Luda Wang, J. Scott Bunch,
Siavash Pourkamali, and Victor M. Bright
Reporter: 朱家君
Date: 2015/4/14

2. Outline
• Introduction
• Theory
• Experiment
• Results (A3 and C6)
• Conclusion

3. Introduction
• Electrically driven thermal-piezoresistive self-sustained
oscillators
• Optical control (HeNe, 632nm wavelength)
→ tune frequency
→ on/off control
• Photoexcitation of charge carriers
→ piezoresistive coefficient change

4. Device (A3, n-type SOI)
in-plane longitudinal mode

5. Theory
• Motional conductance:
(E: temperature dependent)
• Photoexcitation of carriers → silicon’s resistivity ↓
HeNe energy (~1.96 eV) > extrinsic (~0.15 eV)
and intrinsic (~1.12 eV)
• Illumination ↑ , IDC ↑ , power dissipation changed,
Joule heating changed in turn, steady-state temperature

6. Piezoresistance factor P(N,T)
• Piezoresistive coefficient:
1. Total carrier concentration from excited carriers ↑
2. Steady-state temperature changes
• Piezoresistive coefficient ↓
→ gm ↓
→ not satisfied gmRA < -1
→ finally shutoff
carrier concentration

7. Experiment

8. Results (C6, DC=31.61V)
DC current Peak frequency
(1D Lorentzian profile)

9. Results (C6, DC=31.61V)
V(AC, max) Oscillation off/on

10. • Photoexcitation of carriers
→ device resistance ↓
→ DC power dissipation in turn ↓
→ temperature ↓
→ stiffens the Young’s modulus
→ frequency ↑.

11. Results (A3, DC=37.96V)
carrier excitation saturation limit → scattering loss mechanisms to dominate
and cause an increase in electrical resistance

12. Conclusion
• This work demonstrates thermal-piezoresistive oscillators
can be frequency tuned and controllably quenched using
continuous wave HeNe illumination of the structure.
• It is predicated upon direct influence of the piezoresistivity
of the material.
• This method of control potentially offers a unique way of
integrating these devices with on-chip photonic circuitry.

13. END

14. Application