6.1 Conclusions
MOSFET are getting more and more important in current commercial market especially for the RF applications. In this thesis, we have examined the effect of HC stress and oxide breakdown on RF MOSFETs. We also have established a conventional small-signal model for the MOSFETs under HC stress and oxide breakdown.
HCS and OBD all reduce the transconductance, output drain current and enlarge threshold voltage of the MOSFET. Consequently, the high frequency and power characteristics will suffer degradation by those effects. In the first instance, we found that the cut-off frequency and maximum oscillation frequency all decreased after stress. Then the RF output power will suffer degradation after HCS and OBD and we find that the RF power and gain are more robust to HC effects by biasing the gate voltage to higher values. On the other hand, the linearity suffers slight degradation after HCS and OBD if biasing the MOSFET at constant drain current. Thirdly, we found that HCS and OBD influence the noise characteristics of MOSFETs more seriously. Therefore the MOSFET reliability must be a critical concern while designing a low noise amplifier. In addition, unlike degradations of other electric parameters, the minimum noise figure suffered more degradation after HBD than that after HCS and it is due to the additional shot noise source in gate oxide after HBD.
Finally, from observing the small-signal model in chapter 5, we found that the transconductance, drain-to-source resistance, gate-to-source capacitance degrade significantly after HC stress and oxide breakdown. We also confirm that the main leakage path locate at the
gate and source/channel overlap region.
From above discussions,HC stress and oxide breakdown induced degradations on power and noise performances should be taken into consideration in the design of the RF CMOS integrated circuits.
6.2 Future Work
Because the degradations of noise characteristics are serious, we should use the small-signal model to establish the noise model of MOSFETs under HCS and OBD. On the hand, an accurate large-signal model is necessary for the analog and RF IC designer. We should establish a complete large-signal model considering HCS and OBD effect. It may help us to explain the degradations of DC and power characteristics more clearly.
REFERENCES
[1] F. Schwierz, Microwave Transistors: State of the Art in 1980s, 1990s, and 2000s. A Compilation of 100 Top References, TU Ilmenau 2002.
[2] F. Schwierz and J.J. Liou, Semiconductor Devices for Wireless Communications and High-Speed Internet, Proc. SSGRR-2000, pp. 331.1-10, 2000.
[3] F. Schwierz and J.J. Liou, Semiconductor Devices for RF Applications: “Evolution and Current Status”, Microelectron. Reliab, pp. 145-168, 2001.
[4] Pierre H.Woerlee, Mathijs J. Knitel, “RF CMOS Performance Trends,” IEEE Trans.
Electron Devices, Vol 8, pp. 1778-1782,2001.
[5] E.Morifujiet al, “Future Perspective and Scaling Down Roadmap of RF CMOS”, Symposium of VLSI Circuits, pp. 165-166, 1999.
[6] Liou, J.J.; Schwierz, F, “RF MOSFET: Recent Advance and Future Trends” Electron Devices and Solid-State Circuits, pp. 185 – 192, 2003.
[7] H. Hara, Y. Okamoto and H. Ohnuma, “A New Instability in MOS Transistors Caused by Hot Electron and Hole Injection from Drain Avalanche Plasma into Gate Oxide,”
Japanese Journal of Applied Physics, Vol. 9, pp. 1103-1112, 1970.
[8] S. A. Abbas and R. C. Dockerty; “Hot-carriers instability in IGFET’s” Applied Physics Letter, Vol. 27, NO. 3, pp. 147-148, 1975.
[9] T.H. Ning, C. M. Osburn and H. N. Yu “Effect of Electron Trapping on IGFET Characteristics” Journal of Electronic Materials, Vol. 6, NO. 2, pp: 65-76, 1976.
[10] Qiang Li, Yuan Chen, “RF Circuit Performance Degradation Due to Soft Breakdown and Hot-Carrier Effect in Deep-Submicrometer CMOS Technology” IEEE Transcations on Microwave Theory and Techniques, Vol. 49, NO. 9, pp. 1546-1551, 2001.
[11] S. Tam, C Hu“Luck-Electron Model of Channel Hot Electrons Injection in MOSFETs IEEE Transactions on Electron Device, Vol. 31, NO. 9, pp. 1116-1125, 1984.
[12] E. Takeda, Y. Nakagome, H. Kumes, “ A New Hot carrier Injection a Device Degradation in Submicron MOSFETs ＂ IEE Proceedings, Vol. 130, NO.3, pp.144-149,1983.
[13] Taur Ning, “Fundamentals of Modern VLSI Devices” CAMBERIDGE, 1998, chapter 3.
[14] W.L. Ng and N. Toledo, “RF HCI testing methodology and lifetime model establishment,” Reliability Physics Symposium Proceedings (IRPS), pp.1-3, 2004.
[15] Y. T. Yeow, C.H. Ling, “ Observation of MOSFET degradation due to electrical stressing through gate-to-source and gate-to-drain capacitance measurement,” IEEE Electron Device Letters, Vol.12, pp366-369, 1991.
[16] C. Y. Chang and S. M. Sze, “ULSI Devices,” Wiley Interscience, 2000. Chap.6.
[17] R. Van Langevelde and L. F. Tiemeijer, R. J. Havens, M. J. Kniyel, R. F. Roes, P. H.
Woerlee, and D. B. Klassen, “Rf distortion in deep-submicron CMOS technologies,”
IEDM Tech.Dig., p.807-811, 2004.
[18] K. Sanghoon, C. Byounggi, K. Bumman, “Linearity analysis of CMOS for RF application,” IEEE Transactions on Microwave Theory Tech., vol. 51, no. 3, pp.972 – 977, 2003.
[19] S.L. Garverick, and C.G. Sodini, “A simple model for scaled MOS transistors that includes field-dependent mobility,” IEEE J. Solid-State Circuits, vol. 22, no. 1, pp.
111-114, 1987.
[20] B. Toole, C. Plett, and M. Cloutier, “RF circuit implications of moderate inversion enhanced linear region in MOSFETs,” IEEE Transactions on Circuits and Systems I:
Regular Papers, vol. 51, NO. 2, pp. 319 – 328, 2004.
[21] Saman Asgaran, M. Jamal Deen, Chih-Hung Chen, “Analytical modeling of MOSFETs channel noise and noise parameters,” IEEE Trans. Electron Devices, Vol.51, pp.
2109-2114, 2004.
[22] C. Fiegna, “Analysis of gate shot noise in MOSFETs with ultrathin gate oxides,” IEEE Electron Device Lett., vol. 24, NO. 2, pp. 108–110, 2003.
.
[23] G. Dambrine, A. Cappy, F. Heriodore, and E. Playez, "A new method for determining the FET small-signal equivalent circuit " IEEE Trans. Microwave lkeory Tech., Vol 36, pp. 1151-1159. 1988.
[24] S. Lee et al., “A novel approach to extracting small-signal model parameters of silicon MOSFET’s,” IEEE Microwave Guided Wave Lett., Vol. 7, pp. 75-77, 1997.
[25] S. Lee et al., “A small-signal RF model and its parameter extraction for substrate effects in RF MOSFET’s,” IEEE Trans. Electron Devices, vol. 48, pp. 1374–1379, 2001.
[26] S. C. Wang, G. W. Huang, “A Practical Method to Extract Extrinsic Parameters for the Silicon MOSFET Small-Signal Model” 2004 Workshop on Compact Modeling, 2004.
[27] Y. T. Yew, C. H. Ling, “Observation of MOSFET Degradation Due to Electrical Stressing Through Gate-to-Drain Capacitance Measurement,” IEEE Electron Device Letters, Vol.
12, NO.7, pp.366-368, 1991
[28] C. H. Ling, “A study of Hot Carrier Degradation in NMOSFET’s by Gate Capacitance and charge pumping method,” IEEE Transaction on Electron Device, Vol. 42, NO. 7, pp.
1321-1328, 1995.