The physics of amorphous-silicon thin-film transistors

The basic physics underlying the operation and key performance issues of amorphous-silicon thin-film transistors (TFTs) are discussed. The static transistor characteristics are determined by the localized electronic states that occur in the bandgap of the amorphous silicon. The deep states, mostly consisting of Si dangling bonds, determine the threshold voltage, and the conduction band-tail states determine the field-effect mobility. The finite capture and emission times of the deep localized states lead to a dynamic transistor characteristic that can be described by a time-dependent threshold voltage. The transistors also show longer time threshold voltage shifts due to two other distinct mechanisms: charge trapping in the silicon nitride gate insulator and metastable dangling bond state creation in the amorphous silicon. These two mechanisms show characteristically different bias, temperature, and time dependencies of the threshold voltage shift. Illumination of a TFT causes the generation of electron-hole pairs in the space-charge region leading to a steady-state equal flux of electrons and holes and a reduction in the band-bending. In most applications, the photosensitivity should be minimized. The uniformity of large arrays of transistors for display applications is excellent, with variations in the threshold voltage of 0.5-1.0 V. >

[1]  Benjamin Abeles,et al.  Evidence for Exponential Band Tails in Amorphous Silicon Hydride , 1981 .

[2]  D. Anderson,et al.  An improved field-effect analysis for the determination of the pseudogap-state density in amorphous semiconductors , 1981 .

[3]  J. W. Orton,et al.  Characteristics of amorphous silicon staggered-electrode thin-film transistors , 1984 .

[4]  Michael S. Shur,et al.  Physics of amorphous silicon based alloy field‐effect transistors , 1984 .

[5]  I. D. French,et al.  Bias dependence of instability mechanisms in amorphous silicon thin‐film transistors , 1987 .

[6]  M. J. Powell.  Material Properties Controlling the Performance of Amorphous Silicon Thin Film Transistors , 1984 .

[7]  R. Street,et al.  Fast and slow states at the interface of amorphous silicon and silicon nitride , 1986 .

[8]  A. Hourd,et al.  Determination of the extended-state electron mobility in a-Si , 1985 .

[9]  A. J. Snell,et al.  The characteristics and properties of optimised amorphous silicon field effect transistors , 1983 .

[11]  R. Street,et al.  Electronic states at the hydrogenated amorphous silicon/silcon nitride interface , 1984 .

[12]  M. J. Powell,et al.  Defect model of charge transfer doping at a-SiNx:H/a-Si:H interfaces , 1985 .

[13]  C. Hilsum,et al.  Simplified electrode arrangement for TFT-matrix liquid crystal displays , 1986 .

[14]  G. Müller.  On the generation and annealing of dangling bond defects in hydrogenated amorphous silicon , 1988 .

[15]  M. Hijikigawa,et al.  A 14-in.-diagonal full-color a-Si TFT LCD , 1988, Conference Record of the 1988 International Display Research Conference.

[16]  P. L. Comber,et al.  An investigation of the conductivity prefactor in a-Si as a function of Fermi level position using the field-effect experiment , 1987 .

[17]  J. R. Hughes,et al.  Dynamic Characteristics of Amorphous Silicon Thin Film Transistors , 1987 .

[18]  R. Walden.  A Method for the Determination of High‐Field Conduction Laws in Insulating Films in the Presence of Charge Trapping , 1972 .

[19]  M. Powell,et al.  Charge trapping instabilities in amorphous silicon‐silicon nitride thin‐film transistors , 1983 .

[20]  Marshall,et al.  Metastable defects in amorphous-silicon thin-film transistors. , 1986, Physical review letters.

[21]  C. van Berkel,et al.  Resolution of amorphous silicon thin-film transistor instability mechanisms using ambipolar transistors , 1987 .

[22]  C. van Berkel,et al.  Photo‐field effect in amorphous silicon thin‐film transistors , 1986 .

[23]  A. R. Hepburn,et al.  Charge trapping effects in amorphous silicon/silicon nitride thin film transistors , 1987 .

[24]  T. Credelle.  Thin-film transistors for video applications , 1988, Conference Record of the 1988 International Display Research Conference.

[25]  P. Thomas,et al.  A Simple Scheme for Evaluating Field Effect Data , 1980 .

[26]  R. Street,et al.  Hole carrier drift-mobility measurements in a−Si:H, and the shape of the valence-band tail , 1988 .

[27]  Robert A. Street,et al.  Electron drift mobility in amorphous Si: H , 1986 .

[28]  K. Weber,et al.  Temperature-dependent effects in field-effect measurements on hydrogenated amorphous silicon thin-film transistors , 1988 .

[29]  R. Weisfield,et al.  Page-wide a-Si:H TFT arrays for electronic printing and copying , 1988, Conference Record of the 1988 International Display Research Conference.

[30]  R. Schropp,et al.  Instability mechanism in hydrogenated amorphous silicon thin‐film transistors , 1987 .

[31]  M. J. Powell,et al.  Annealing and light induced changes in the field effect conductance of amorphous silicon , 1982 .

[32]  J. R. Hughes,et al.  A 6-in. full color liquid-crystal television using an active matrix of amorphous-silicon TFTs , 1988 .

[33]  J. R. Hughes,et al.  Deep trapping controlled switching characteristics in amorphous silicon thin‐film transistors , 1989 .

[34]  R. Street.  The origin of metastable states in a-Si:H , 1988 .

[35]  J. R. Hughes,et al.  Time and temperature dependence of instability mechanisms in amorphous silicon thin-film transistors , 1989 .

[36]  M. J. Powell.  Analysis of field-effect-conductance measurements on amorphous semiconductors , 1981 .

[37]  M. Shur,et al.  New high field‐effect mobility regimes of amorphous silicon alloy thin‐film transistor operation , 1986 .

[38]  T. Suzuki,et al.  a-Si:H TFT Driven Linear Image Sensor , 1987 .

[39]  R. Schropp,et al.  A SELF-CONSISTENT ANALYSIS OF TEMPERATURE-DEPENDENT FIELD-EFFECT MEASUREMENTS IN HYDROGENATED AMORPHOUS-SILICON THIN-FILM TRANSISTORS , 1986 .

[40]  Jackson,et al.  Creation of near-interface defects in hydrogenated amorphous silicon-silicon nitride heterojunctions: The role of hydrogen. , 1987, Physical review. B, Condensed matter.

[41]  Alaa Ghaith,et al.  Amorphous-silicon field-effect device and possible application , 1979 .

[42]  J. Pritchard,et al.  The effect of surface states and fixed charge on the field effect conductance of amorphous silicon , 1983 .