50-Å gate-Oxide MOSFET's at 77 K

While hot-carrier-induced degradation is aggravated at cryogenic temperature, a very thin gate-oxide (52-Å) device can still tolerate a 3-V power-supply voltage at 77 K. Hot-carrier-induced degradation may not be the limiting factor in choosing the power-supply voltage and special drain structures may be necessary for very thin gate MOSFET's even at 77 K. However, mobility reduction at high VGis more severe both at lower temperatures and for thinner oxides. Electron mobility appears to be oxide-thickness-dependent at 77 K. The dependence of the electron mobility on the normal field is so strong that it results in unusual I-V characteristics such as negative transconductance at 77 K for an oxide field above 3 MV/cm. The I--V characteristics have been modeled with a mobility dependence on VGSof the form µn ∞ (1 + η(VGS- Vt/Tox)²+ (E/Ec))^-1for 52-Å devices.     

Effects of interfacial Oxide layer on short-channel polycrystalline source and drain MOSFET's

Using a novel self-alignment approach, the characteristics of polycrystalline source and drain MOSFET's with and without a deliberately grown oxide under the polycrystalline regions are compared. The interfacial oxide is shown to suppress short-channel effects in the shortest channel devices studied, but this improvement is at the expense of increased source-to-drain contact resistance in the present devices. The devices without the interfacial oxide are also expected to have superior hot-carrier performance.     

Effects of ionizing radiation on n-channel MOSFET's fabricated in zone-melting-recrystallized Si films on SiO2

We have investigated the effects of irradiation with 1.5 MeV electrons on the electrical characteristics of n-channel MOSFET's fabricated in zone-melting-recrystallized Si films on SiO2-coated Si substrates. With a -15 V bias applied to the Si substrate during irradiation and device operation, the subthreshold leakage current remains below 0.2 pA/µm (channel width) for ionizing doses up to 10⁶rad(Si). The negative substrate bias also reduces the shift of threshold voltage to less than 0.3 V for devices with 50 nm-thick gate oxide.     

Analysis of short-channel MOSFET's with field-dependent carrier-drift mobility

MOSFETI_{D}-V_{D}characteristics have been investigated, using two-dimensional analysis which includes field-dependent carrier-drift mobility. It is predicted that drain current is affected by the relationship between carrier-drift velocity and electric-field strength. Reduction mechanisms for normalized drain current and current saturation voltage for short-channel MOSFET's have become clear. In the light of the above analysis, an analytical model is presented. The model is simple, in spite of taking the field-dependent carrier-drift mobility and the proper current saturation concept into account. Predicted results are in good agreement with experimental data down toL = 1µm.     

New O II 6640-Å laser line

A prominent red laser line has been observed in oxygen and air at a wavelength of 6640.2 ± 1 Å. This line corresponds to the3p^{2}Smin{1/2}max{0}-3s^{2}P_{1/2}at 6640.90 Å of the O II spectrum. It is the strongest member of the observed emission lines close to the laser line.     

Efficient generation of continuously tunable coherent radiation in the 2460-2650-Å spectral range

Continuously tunable coherent radiation in the 2460- 2650-Å spectral range has been achieved by second harmonic generation (SHG) of a dye laser in a 90° phase-matched ADP crystal, temperature tuned between-116°C and 52°C. The 8.4-percent conversion efficiency obtained at a fundamental power of 9.6 kW is approximately 5 times larger than that reported earlier for SHG at these wavelengths.     

Hot-electron limited operating voltages for 0.8-µm MOSFET's

The maximum allowable operating voltage limited by hot-electrons for 0.8-µm MOSFET's, VGS= VDS, is determined to be 5.5 V at room temperature with VSUB= -2 V, as a result of long-term stress aging. Slow and fast threshold-voltage shifts are observed depending on stress conditions, i.e., the amount of hot-electrons injected into the gate SiO2. Generation of interface trapped charges at the Si-SiO2interface near the drain junction is suggested as a main cause for degradation.     

Two-dimensional analytical modeling of threshold voltages of short-channel MOSFET's

We present an analytical model of the threshold voltage of a short-channel MOSFET based on an explicit solution of two-dimensional Poisson's equation in the depletion region under the gate. This model predicts an exponential dependence on channel length (L), a linear dependence on drain voltage (VD), and an inverse dependence on oxide capacitance (εox/tox). An attractive feature of this model is that it provides an analytical closed-form expression for the threshold voltage as a function of material and device parameters (tox, VD, L, substrate bias, and substrate doping concentration) without making premature approximations. Also, this expression reduces to the corresponding expression for long-channel devices.     

Analytical modeling of the subthreshold current in short-channel MOSFET's

In this paper an analytical model for subthreshold current for both long-channel and short-channel MOSFET's is presented. The analytical electrostatic potential derived from the explicit solution of a two-dimensional Poisson's equation in the depletion region under the gate for uniform doping is used. The case for nonuniform doping can easily be incorporated and will be published later. The results are compared to a numerical solution obtained by using MINIMOS, for similar device structures. An analytical expression for the channel current is obtained as a function of drain, gate, substrate voltages, and device parameters for devices in the subthreshold region. The short-channel current equation reduces to the classical long-channel equation as the channel length increases.     

Isotope shifts in the 4416-Å cadmium laser

Isotope shifts in Cd¹¹², Cd¹¹⁴, and Cd¹¹⁶have been measured using enriched isotopes in a cadmium laser. Preparatory measurements using natural cadmium showed an anomalous change from a double-peaked spectral profile to a single-peaked profile when the active tube length was doubled.     

Threshold and punchthrough behavior of laterally nonuniformally doped short-channel MOSFET's

Predictions of gate threshold voltage and punchthrough voltage have been made for short-channel VDMOS and UMOS field-effect transistors using exact, two-dimensional numerical analysis. In these devices the doping concentration varies laterally from source to drain. The threshold voltage is found to be related to the maximum value of channel doping. This correspondence becomes poorer as the channel length is diminished since punchthrough current begins to influence the threshold voltage for short-channel devices. Surface punch-through is predicted for the VDMOSFET whereas bulk punchthrough is found in the UMOS device. A correspondence between the results of two-dimensional computer simulation of punchthrough and the estimations of one-dimensional simplified theory is found.     

Effects of electric fields on annealing of radiation damage in MOSFET's

Radiation damage inp-channel MOS devices by 1.5 MeV electrons has been studied by thermal annealing in conjunction with electric fields between the metallic gate and the substrate. Both positive and negative gate biases retard the process of annealing. Annealing with negative gate bias reveals 1) that during thermal annealing the majority of the electrons that recombine with the positive charge in the oxide originate from the conduction band of the silicon, and 2) that during irradiation a great number of ionized electrons that remain in the oxide do not recombine with the holes, but are trapped in weakly bound states. The effect of positive bias on annealing of radiation damage is obscured by the positive charge induced due to positive bias-temperature treatment alone. No effect of drain-to-source potential on annealing has been observed.     

The output power of a 6328-Å He-Ne gas laser

Expressions are derived for the output power of a gas laser in single-mode operation. This theory is then extended to multimode operation where the mode spacing is less than the pressure-broadened "natural" atomic linewidth. Using measured values for the linewidth and saturation parameters, these formulas are used to predict 6328-Å output power for a He-Ne laser as a function of laser gain, cavity loss, and output coupling. Experiments are reported which show good agreement with the theoretical predictions, and it is concluded that the theory presented here is adequate to describe the main features of the power output behavior of a 6328-Å He-Ne gas laser.     

Effects of ionizing radiation on glow discharge detectors

Glow discharge detectors in the abnormal glow mode can be used as sensitive detectors of microwave and millimeter wave radiation even in the presence of very intense γ ionizing radiation fields where semiconductor devices cannot operate. In the subnormal glow mode, glow discharge detectors give promise of being able to monitor ionizing radiation fields so intense that the usual electronic detectors saturate.     

A theoretical description of the 5106-Å pulsed copper vapor laser

A theoretical model that accounts for the experimentally observed features of the 5106-Å pulsed copper vapor laser has been devised. The electron excitation and ionization cross sections used in the theory were calculated by the use of the classical Gryzinski-type methods.     

Photopreionization of the 3371-Å pulsed N2laser

Photopreionization of the 3371-Å pulsed N2laser by use of a seed gas of low ionization threshold and flashlamp excitation is observed to result in increased laser output and reproducibility. Preionization also increases the range of permissible operating pressures, enabling operation with atmospheric-pressure mixtures of N2and He without reduced intensity.     

Analysis of hot-carrier-induced aging from 1/f noise in short-channel MOSFET's

The 1/f noise of short-channel n-type MOSFET's is measured in the weak inversion regime before and after an electrical stress. The noise increase which follows the aging is shown to be due to an electrically induced generation of traps in the gate oxide rather than fast interface states. Noise experiments prove that the degradation occurs in a narrow region (less than 50 nm) near the drain. Created traps also appear to have an inhomogeneous energy profile.     

Determination of the spatial variation of interface trapped charge using short-channel MOSFET's

Previous measurements of interface trapped charge (ITC) by charge pumping used long-channel metal gate transistors. In this paper charge pumping is extended to short-channel Self-aligned polysilicon gate transistors and used to determine the spatial variation of ITC on wafers. Only the MOSFET gate area and a pulse frequency are required to calculate ITC density from the charge pumping current. In previous work, with long-channel devices, it appears that some investigators used the design dimension of metal gate devices and others used the metallurgical channel length of the transistors to calculate gate area. Two-dimensional simulation of the charge pumping measurement showed that, for a sufficient applied pulse height voltage, the correct area is obtained if the polysilicon gate length and width asmeasured are used. When the process-induced variation of the polysilicon gate length is included in the measurement analysis, no systematic variation of ITC is observed across 5 cm wafers. The charge pumping measurement technique on short-channel MOSFET's can be used to resolve the spatial variation of ITC if the area variations are correctly handled. The measurement of ITC is linear with frequency from 1 kHz to 1 MHz, indicating that the emission time constant of the fast states measured using this method is ≤10^-6s. A variation of ITC with channel lengths is also observed. This variation could not be detected using large area devices such as capacitors, but will have important consequences for short-channel MOSFET's.