Transient pass-transistor leakage current in SOI MOSFET's

This paper reports an accurate method of measuring the anomalous leakage current in pass-gate MOSFET's unique to SOI devices. A high-speed measurement setup is used to provide experimental results, and to quantify the magnitude of leakage. Particularly, great care is taken to measure only the device leakage current and not the currents due to parasitic capacitances. Systematic influences of different factors such as temperature, bias, device history, and device structure on this leakage current are experimentally established,     

Temperature dependence of hot-electron-induced degradation in MOSFET's

The temperature dependence of MOSFET degradation due to hot-electron injection has been studied. The slower degradation rate at elevated temperature at fixed stressing bias follows the substrate current level which is reduced mainly by lower localized electric field rather than lower ionization coefficient (both are caused by enhanced phonon scattering). The actual degradation rate at the constant substrate current level is slightly higher at elevated temperatures, indicating an enhanced interface-state generation mechanism. This temperature dependence provides a simple relationship between device degradation and substrate current at various temperatures.     

Temperature dependence of the channel hot-carrier degradation ofn-channel MOSFET's

The generation of fast interface traps due to channel hot-carrier injection in n-channel MOS transistors is investigated as a function of stress temperature. The relative importance of the mechanisms for the generation of fast interface traps by hot electrons and hot holes is shown to be independent of the temperature. In all cases the generation of fast interface traps is slightly reduced at lower temperatures. The degradation of transistor I_d-V_g characteristics, on the other hand, is strongly enhanced at lower temperatures. This is explained by a previously suggested model on the temperature dependence of the influence of the local narrow potential barrier, induced at the drain junction as a result of degradation, on the reverse-mode current characteristics. It is shown that only a minor part of the large current reduction at low temperatures can be ascribed to enhanced electron trapping     

Temperature dependence of gate induced drain leakage current insilicon CMOS devices

The temperature dependence of the gate induced drain leakage (GIDL) current in CMOS devices is investigated from 20K up to 300K. It is shown that, at sufficiently high electric field, the conventional band-to-band tunnelling GIDL current law is applicable down to near-liquid helium temperatures for both nand p-channel devices. The exponential factor B of the GIDL current law is found to be nearly independent of temperature. Moreover, the decrease of the GIDL current as the temperature is lowered, is shown to originate from the temperature variation of the pre-exponential coefficient A of the GIDL current law     

Investigation of anomalous leakage current in mesa-isolated SOIMOSFETs

The mechanism of an anomalous leakage current in mesa-isolated SOI NMOSFETs in the short-channel region was analyzed. The enhanced diffusion of the source-drain impurities was observed in the mesa edge region by Energy Dispersive X-ray Spectroscopy (EDX) analysis. Moreover, using high-resolution TEM observation, it was found that there were no crystalline defects in the edge region. The frequency of leakage currents in short-channel MOSFETs was higher than that of long-channel MOSFETs. The level of leakage current was not changed by the gate voltage and back gate voltage, and the activation energy of the leakage current was almost 0 eV. According to these results, it is concluded that the origin of the anomalous leakage current is the enhanced diffusion of source-drain impurities     

Temperature dependence of MOSFET substrate current

Hitherto, theoretical models for MOSFET substrate current predicted that substrate current is a strong function of temperature. However, experimental data presented in this and previous studies show that the ratio of substrate current to drain current is insensitive to temperature over the range 77 to 300 K. The authors propose a modified model for an electron mean-free path (MFP) in the substrate current based on the concept of energy relaxation. The different between the energy and momentum relaxation MFP is clarified, and it is shown that a substrate current model with modified MFP can explain the temperature dependence of the substrate current     

Temperature dependence of the saturation current of MOST's

The saturation current ofn-enhancement silicon MOST's has been investigated as function of temperature. The results are in reasonable agreement with a simple theoretical expression which takes into account the field dependence of electron mobility. It is shown that the effective incremental mobility becomes fairly independent of temperature, and varies inversely proportional to the gate voltage VG, ifmicro V_{G}/upsilon_{s}Lis about unity, where µ is the low-field drift mobility, υs, is the saturation drift velocity, andLis the channel length.     

Subthreshold current of dual-gate MOSFET's

The subthreshold conduction in dual-gate MOS transistors is investigated. The subthreshold current is calculated both in the long-channel case and the short-channel case by means of simple models. Good agreement is found between theory and experimental results obtained through measurements on overlapping-gate n-channel devices. As an application of the subthreshold current analysis, the low-frequency transfer inefficiency in bucket-brigade devices (BBD's) is evaluated. The theoretical result agrees well with measurements carried out on p-channel nonoverlapping-gate devices.     

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T ³ in the case of Auger recombination.     

Short-channel MOSFET's in the punchthrough current mode

Results of two-dimensional device analysis are compared with experiment for 0.8-µm Si-gate ion-implanted MOS devices operated under conditions of punchthrough transport. Characterization of the punchthrough mode of device operation (a critical factor which limits the maximum drain voltage of submicron MOS VLSI devices) with experiment and simulation has shown that the observed power-law dependence of IDSversusV_{DS} (V_{GS} = V_{SB} = 0)is related to the drain-induced barrier-height lowering. Results of the simulation show the dependence of the punchthrough current upon the range and maximum doping level of the channel implantation. Increasing the substrate-bias or applying a negative-gate voltage is shown to increase the punchthrough voltage. This simulation, which combines results of the process-simulation program (SUPREM) and device-simulation program (CADDET), is shown to predict the behavior of this mode of operation where previous one-dimensional theory has failed.     

Total dose dependence of radiation-induced leakage current in ultra-thin gate oxides

Radiation-induced leakage current (RILC) has been studied on ultra-thin gate oxides (4 and 6 nm) irradiated with 8 MeV electrons. Both RILC and stress-induced leakage current (SILC) have been fitted with the same Fowler–Nordheim law, suggesting that RILC and SILC have similar conduction mechanisms. The RILC dependence from total dose during irradiation has been analysed and compared with the SILC dependence from the cumulative injected charge. Different growth laws of RILC and SILC have been found in the two cases. The intensity of positive and negative RILC also depends on the applied gate bias voltage during irradiation, probably reflecting different distributions of the oxide traps mediating the trap assisted tunnelling. Finally, we have presented the first evidence of a quasi-breakdown phenomenon due to ionizing radiation.     

Temperature dependence of the reverse current in Schottky barrier diodes

The temperature dependences of the current I in reverse-biased Al/SiO₂/n-Si, Al/SiO₂/n-GaAs and Al/n-GaAs (with the native oxide) structures are measured. It is established that these dependences all have the property that the thermal activation energy decreases with increasing applied voltage and that at higher voltages the plots of ln I versus 1/T deviate from straight lines. The results can be explained on the basis of the fact that the current through the barrier is due to electron tunneling from surface states into the conduction band of the semiconductor. The field intensity in the Schottky barrier and the density of surface electron states in the interfacial layer of the semiconductor are estimated by comparing the experimental results with a tunneling theory that takes into account the effect of the semiconductor lattice phonons on the tunneling probability. Fiz. Tekh. Poluprovodn. 32, 882–885 (July 1998)     

Temperature dependence of the threshold current for InGaAlP visiblelaser diodes

The temperature dependence of the threshold current for InGaAlP visible-light laser diodes was investigated from the standpoint of gain-current characteristics. The dependence of the light output power versus the current characteristic on the cavity length was evaluated for a 40-μm-wide InGaP-InGaAlP broad-stripe laser in the temperature range between -70 and 90°C. The threshold-current density dependence on the cavity length shows that a linear-gain approximation is suitable for this system. A minimum threshold-current density of 860 A/cm² was achieved at room temperature with a cavity length of 1160 μm. The internal quantum efficiency decreased in the temperature range higher than -10°C, which affected the excess threshold-current increase and the decrease in the characteristic temperature at this temperature range     

Tunneling leakage current in oxynitride: dependence onoxygen/nitrogen content

It is widely known that the addition of nitrogen in silicon oxide, or the addition of oxygen in silicon nitride, affects its reliability as a gate dielectric. The authors examine the gate leakage current as a function of the oxygen and nitrogen contents in ultrathin silicon oxynitride films on Si substrates. It is shown that, provided that electron tunneling is the dominant current conduction mechanism, the gate leakage current in the direct tunneling regime increases monotonically with the oxygen content for a given equivalent oxide thickness (EOT), such that pure silicon nitride passes the least amount of current while pure silicon oxide is the leakiest     

Stress-induced double-hump substrate current in MOSFET's

Asymmetries in substrate current characteristics due to hot-electron stressing have been observed in short-channel n-MOSFET's. Due to the localized nature of trapped charges or interface traps as a result of hot-electron stressing, transistors can show single-peak or double-hump substrate current characteristics under normal- or reverse-mode measurements. Two-dimensional simulations indicate that a high lateral electric field is generated near the source when the negative charges are trapped there. This electric field is responsible for the observed double-hump substrate current and enhanced gate current injection under reverse-mode measurements for the stressed transistors.     

Temperature dependence of the threshold current density of aquantum dot laser

Detailed theoretical analysis of the temperature dependence of threshold current density of a semiconductor quantum dot (QD) laser is given. Temperature dependences of the threshold current density components associated with the radiative recombination in QDs and in the optical confinement layer (OCL) are calculated. Violation of the charge neutrality in QDs is shown to give rise to the slight temperature dependence of the current density component associated with the recombination in QD's. The temperature is calculated (as a function of the parameters of the structure) at which the components of threshold current density become equal to each other. Temperature dependences of the optimum surface density of QD's and the optimum thickness of the OCL, minimizing the threshold current density, are obtained. The characteristic temperature of QD laser T_o is calculated for the first time considering carrier recombination in the OCL (barrier regions) and violation of the charge neutrality in QDs. The inclusion of violation of the charge neutrality is shown to be critical for the correct calculation of T_o. The characteristic temperature is shown to fall off profoundly with increasing temperature. A drastic decrease in T_o is shown to occur in passing from temperature conditions wherein the threshold current density is controlled by radiative recombination in QD's to temperature conditions wherein the threshold current density is controlled by radiative recombination in the OCL. The dependences of T_o on the root mean square of relative QD size fluctuations, total losses, and surface density of QDs are obtained     

Leakage current characteristics of offset-gate-structure polycrystalline-Silicon MOSFET's

Leakage current characteristics of offset-gate-structure polycrystalline-silicon (poly-Si) MOSFET's are studied as a function of dopant concentration Noffin offset-gate regions. Leakage current markedly decreases from 1 × 10^-9to 2 × 10^-11A at VD= 10 V as Noffis varied from 1 × 10¹⁸to 1 × 10¹⁷cm^-3. A maximum ON/OFF current ratio of 10⁸is obtained at 1 × 10¹⁷cm^-3. Calculations based on a quasi-two-dimensional model indicate that the reduction of leakage current is attributable to a decrease of the maximum lateral electric field strength in the drain depletion region. An analysis of the leakage current characteristics in terms of carrier emission from grain-boundary traps implies that thermonic emission accompanied by thermally assisted tunneling could be the dominant mechanism in determining leakage current.     

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.     

Temperature dependence of threshold current of GaAs quantum well lasers

The radiative recombination rate in a quantum well structure is calculated using a constant density of states and the k-selection rule. This calculation shows that the threshold current of a GaAs quantum well laser has low temperature sensitivity (T0 ? 330 K for T > 300 K).