Total Dose Effect (TDE) on solid state devices is of serious concern as it changes the electrical properties leading to degradation of the devices and failure of the systems associated with them. Ionization caused due to TDE in commercial P-channel Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) has been studied, where the failure mechanism is found to be mainly a result of the changes in the oxide properties and the surface effects at the channel beneath the gate oxide. The threshold voltage of the MOSFETs was found to shift from ？0.69？V to ？2.41？V for a total gamma dose of 1？Mrad. The net negative threshold shifts in the irradiated devices reveal the major contribution of oxide trapped charges to device degradation. The radiation induced oxide and interface charge densities were estimated through subthreshold measurements, and the trap densities were found to increase by one order in magnitude after a total gamma dose of 1？Mrad. Other parameters like transconductance, subthreshold swing, and drain saturation current are also investigated as a function of gamma dose. 1. Introduction In recent years, one can observe a tremendous increase in the usage of electronic instrumentation for nuclear and space research, and it is often susceptible to high ionizing radiations in space. Considerable attention must therefore be given to possible effects of such an environment on electronic devices. Gamma rays are one of the basic radiation sources used to test the device for space applications. Gamma rays interact with matter in three different ways: photoelectric effect, compton scattering, and pair production. In silicon, the photoelectric effect dominates at photon energies less than 50？keV, and pair production dominates at energies greater than 20？MeV with Compton scattering dominating in the intervening energy range [1]. MOSFETs being widely used in space systems because of their faster switching speeds and simple drive requirements are very sensitive to ionizing gamma radiations. The high threshold voltage shifts caused due to trapped charges reduce the switching speed and also modify the other charge dependent properties like transconductance and mobility [2, 3]. The ionization effects in these devices can be related to either the total amount of radiation that is absorbed (total dose) or the rate at which radiation is absorbed (dose rate) [4]. In the present experiment, the devices are evaluated for total dose effects. Of most concern in the total dose effects is the creation of hole electron pairs in silicon dioxide. In any silicon technology
References
[1]
G. E. Schwarze and A. J. Frasca, “Neutron and gamma irradiation effects on power semiconductor switches,” in Proceedings of the 25th Intersociety Energy Conversion Engineering Conference (IECEC '90), pp. 30–35, August 1990.
[2]
A. P. G. Prakash, S. C. Ke, and K. Siddappa, “High-energy radiation effects on subthreshold characteristics, transconductance and mobility of n-channel MOSFETs,” Semiconductor Science and Technology, vol. 18, no. 12, pp. 1037–1042, 2003.
[3]
Y. H. Lho and K. Y. Kim, “Radiation effects on the power MOSFET for space applications,” ETRI Journal, vol. 27, no. 4, pp. 449–452, 2005.
[4]
J. E. Gover and T. A. Fischer, “Radiation-hardened microelectronics for accelerators,” IEEE Transactions on Nuclear Science, vol. 35, no. 1, pp. 160–165, 1987.
[5]
N. Mohan, Project Report ECE 709, University of Waterloo.
[6]
D. K. Schroder, Semiconductor Material and Device Characterization, Wiley Interscience, New York, NY, USA, 1990.
[7]
C.-Y. Chen, J.-W. Lee, S.-D. Wang et al., “Negative bias temperature instability in low-temperature polycrystalline silicon thin-film transistors,” IEEE Transactions on Electron Devices, vol. 53, no. 12, pp. 2993–2999, 2006.
[8]
P. J. Mc Whorter and P. S. Winokur, “Simple technique for separating the effects of interface traps and trapped‐oxide charge in metal-oxide-semiconductor transistors,” Applied Physics Letters, vol. 48, no. 2, p. 133, 1986.
[9]
T. R. Oldham and F. B. McLean, “Total ionizing dose effects in MOS oxides and devices,” IEEE Transactions on Nuclear Science, vol. 50, no. 3, pp. 483–499, 2003.
[10]
P. M. Lenahan and P. V. Dressendorfer, “Hole traps and trivalent silicon centers in metal/oxide/silicon devices,” Journal of Applied Physics, vol. 55, no. 10, pp. 3495–3499, 1984.
[11]
P. J. McWhorter, D. M. Fleetwood, R. A. Pastorek, and G. T. Zimmerman, “Comparison of MOS capacitor and transistor postirradiation response,” IEEE Transactions on Nuclear Science, vol. 36, no. 6, pp. 1792–1799, 1989.
[12]
P. M. Lenahan, N. A. Bohna, and J. P. Campbell, “Radiation-induced interface traps in MOS devices: capture cross section and density of states of Pb1 silicon dangling bond centers,” IEEE Transactions on Nuclear Science, vol. 49, no. 6, pp. 2708–2712, 2002.
[13]
T. P. Ma and P. V. Dressendorfer, Ionizing Radiation Effects in MOS Devices and Circuits, John Wiley & Sons, New York, NY, USA, 1989.
[14]
F. A. S. Soliman, A. S. S. Al-Kabbani, M. S. I. Rageh, and K. A. A. Sharshar, “Effects of electron-hole generation, transport and trapping in MOSFETs due to γ-ray exposure,” Applied Radiation and Isotopes, vol. 46, no. 12, pp. 1337–1343, 1995.
