Change In Gate Voltage Research Articles

Determination of the effective mass of ballistic electrons in thin silicon oxides films using tunneling current oscillations

A new, simple and accurate method is proposed for the determination of the effective electron mass in thin insulator films from the current–voltage characteristics in fields of the ballistic electron emission regime. The effective mass of electrons was evaluated for oxide films of metal-oxide-semiconductor structures. The effective ballistic electron mass near the conduction band edge of silicon dioxide for different structures changes from 0.52 to 0.84 m 0 and the experimental data show that the value of the effective mass of the ballistic electron can be treated as a constant while the gate voltage changes at least within a certain voltage range.

Optical spectroscopy of negative-U centers

The identification of strongly correlated double electron local sites in semiconductors usually requires a nonequilibrium situation in order to observe a single occupied state of a local site. We present a way of a direct observation of negative-U centers by means of a single photon optical transition from band states into local states provided controlled occupancy of local levels via doping the semiconductor or via change of the gate voltage. The photoabsorption spectrum shows single and double electron transitions as the consequence of the hybridization of local states and band electron states. The value of the correlation energy in localized states determine positions and intensities of peaks while the occupancy of local levels reflects itself in the line shape. A qualitative comparison with available data on installed atoms as possible double electron centers in semiconductors is made.

Silicon Single Electron Transistors with Single and Multi Dot Characteristics

AbstractSilicon single electron transistors (SET) with side gate have been fabricated on a heavily doped silicon-on-insulator (SOI) substrate. Samples demonstrate two types of characteristics: some of them demonstrate multiple dot behavior and one demonstrates single dot behavior in a wide temperature range. SETs demonstrate oscillations of drain-source current and changes in the width of the Coulomb blockade region with change of gate voltage at least up to 100 K. At temperature below 20 K long-term oscillations (relaxation) of source-drain current after switching the gate voltage has been observed in both multiple dot and single dot samples. Illumination affects both the characteristics of the SETs and the relaxation process. Telegraph noise has been observed in a definite range of source-drain and gate voltages.

Under-Gate Triode Type Field Emission Displays with Carbon Nanotube Emitters

ABSTRACTA new structure of triode type field emission displays based on single-walled carbon nanotube emitters is demonstrated. In this structure, gate electrodes are situated under cathode electrodes with an in-between insulating layer, so called under-gate type triode. Electron emission from the carbon nanotube emitters is modulated by changing gate voltages. A threshold voltage is approximately 70 V at the anode bias of 275 V.

Magnetocapacitance in quantum Hall regime with external dc current

We have investigated the magnetocapacitance between gates and two dimensional electron system in a GaAs/AlGaAs heterostructure with an external dc current at quantum Hall (QH) plateau regime. With increasing dc current, the minimum values of capacitance at QH plateaux increase and the range of magnetic fields showing the capacitance minima decreases. The electrons excited by the external dc current enhance the σ XX which causes the breakdown of the QH effect. In a certain magnetic field and current direction, the capacitance dip at QH plateau splits into two valleys with dc current. These results are considered to be due to the change of effective gate voltage caused by the current. The breakdown current of the QH effect evaluated by the resistance measurement is several times larger than that obtained by the dc current dependence of the magnetocapacitance, since the capacitance is very sensitive to the residual σ XX. The vanishing of the capacitance minima may be the precursor of QH breakdown.

Coulomb-glass-like behavior of ultrathin films of metals

A field-effect conductance-modulation experiment has been performed on ultrathin films of metals deposited onto amorphous germanium substrates. For the thinnest films at the lowest temperatures, the conductance exhibits logarithmic decay, memory, aging, and hysteretic effects in its response to changes in gate voltage. These glasslike phenomena disappear above a characteristic temperature, and become immeasurable as film thickness is increased.

Investigation of interface traps in LDD pMOST's by the DCIV method

Interface traps in submicron buried-channel LDD pMOSTs, generated under different stress conditions, are investigated by the direct-current current-voltage (DCIV) technique. Two peaks C and D in the DCIV spectrum are found corresponding to interface traps generated in the channel region and in the LDD region respectively. The new DCIV results clarify certain issues of the underlying mechanisms involved on hot-carrier degradation in LDD pMOSTs. Under channel hot-carrier stress conditions, the hot electron injection and electron trapping in the oxide occurs for all stressing gate voltage. However, the electron injection induced interface trap spatial location changes from the LDD region to the channel region when the stressing gate voltage changes from low to high.

Charge trap generation in LPCVD oxides under high field stressing

The degradation of low pressure chemical vapor deposited (LPCVD) oxides, prepared using silane and tetra ethyl ortho silicate (TEOS) as the source, has been investigated under high field stressing. The LPCVD oxides exhibit enhanced conductivity for the Fowler-Nordheim tunneling current, which is modeled as an effective lowering of potential barrier at the injecting electrode. The charge to breakdown (Q/sub bd/) of LPCVD oxides depends on both the deposition chemistry and post deposition annealing condition. The change in interface-state density (/spl Delta/D/sub it/), flatband voltage (/spl Delta/V/sub fb/), and gate voltage (/spl Delta/|V/sub g/|) during constant current stressing are studied to identify the degradation mechanism. We see a very good correlation between Q/sub bd/ and /spl Delta/|V/sub g/|, indicating that the degradation in LPCVD oxides is dominated by bulk trap generation and subsequent charge trapping. We present a detailed theoretical analysis to substantiate this.

Low-frequency noise in very high mobility modulation-doped structures

We report here on the observation of low-frequency (1–100 Hz) noise characteristics as a function of current in very high mobility four-terminal structures at 4.2 K. At low currents, the noise levels are too low to be observed with our measurement system. When the mobility is decreased by a change in gate voltage, or when the injected current is increased, noise levels increased. At currents where excess noise is observable, the channel current-voltage characteristics are nonlinear and the noise current dependence is superquadratic. The steep current-dependence results from the degradation of mobility due to electron heating, with the subsequent rapid noise increase due to optical phonon scattering.

An Ionic Liquid‐Channel Field‐Effect Transistor

The basic theory and first experimental results of a new microfabricated ionic liquid‐channel field‐effect transistor (ILCFET) are presented. The ILCFET resembles a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) except that the current flowing from the source to the drain is carried in thin channels by ions of a liquid electrolyte. In MOSFETs the gate‐induced electric field changes the channel concentration of only one mobile carrier, the holes or the electrons. In ILCFETs the concentrations of both cations and anions are altered. The devices that we have built have channels 0.088 μm thick and 300, 600, and 900 μm long. The basic steady‐state theory predicts that for a channel thickness of 8 Debye lengths and a gate voltage change from 0 to 25 V (representing a potential change of 150 mV at the solid/liquid interface) the steady‐state anion/cation ratio increases by a factor of 17.8. For a glycerol solution of , the channel conductance increases correspondingly by a factor of 5.2. The transient response to a gate voltage step is modeled as a gate capacitance charging current followed by slower ambipolar diffusion. Both processes are described by the diffusion equation. Measurements have been made of conductance vs. gate voltage, gate capacitance charging current, and slow conductance changes due to diffusion for different types of glycerol solutions. Whereas the gate current transient response data agree well with theory, the long‐term transient response data indicate that phenonema other than ambipolar diffusion are present. Finally, the slopes of the channel conductance vs. gate voltage curves are less than predicted by the basic theory.

Demonstration of the heterostructure field-effect transistor as an optical modulator

A new semiconductor waveguide absorption modulator is demonstrated utilizing the heterostructure field-effect transistor structure. The modulator of 300 μm length and 10 μm width achieves an extinction ratio of 8 for a gate voltage change of 2.5 V and an absorption change greater than 2300 cm−1. The transistor transconductance is 92 ms/mm for a 1 μm device and an identical structure has been reported as an edge-emitting laser providing an ideal combination for optoeletronic integration.

Anomalous drain-induced barrier lowering in short channel NMOS devices at 77 K

Anomalous results on drain-induced barrier lowering (DIBL) in short channel NMOS devices at 77K are presented. It was found that for devices with channel lengths 0.7 and 1.3 μm, the DIBL measured by the change in gate voltage induced by a unit change in drain voltage at a fixed drain current was worse at 77K than at 300K. However, for devices that were either shorter than 0.7 μm or longer than 1.3 μm, DIBL was improved at 77K compared with 300K. The experimental results were in good agreement with the numerical calculations using MINIMOS 4.0.

Unusually abrupt switching in submicrometer thin-film transistors using a polysilicon film with enhanced grain size

Unusually abrupt drain current change observed in polysilicon thin-film transistors (TFTs) with a channel length and width of 1 mu m or smaller is discussed. The polysilicon used to fabricate the devices was deposited by low-pressure chemical vapor deposition (LPCVD) and the grain size of the film was enhanced by silicon ion implantation followed by a low-temperature anneal. The TFTs exhibited an abrupt drain current change of more than five orders of magnitude for a corresponding gate voltage change of less than 40 mV. A self-limiting positive feedback loop due to impact ionization currents and/or a parasitic bipolar effect are suggested as possible explanations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An extremely abrupt switching phenomenon in small-dimension polysilicon TFT structures with enhanced grain size

Summary form only given. In the course of exploring the transfer characteristics in small-dimensional polysilicon TFTs (thin-film transistors), the authors found an extremely abrupt drain current change which cannot be explained by the existing TFT models. The measured devices are coplanar-type, n-channel polysilicon TFTs with channel widths and lengths, W and L, ranging from 20 mu m to half a micrometer. The authors measured the (drain current)-(gate voltage) characteristics in TFTs with various L and W applying a drain voltage of 5.0 V. It was found that the subthreshold slope became steeper as the channel dimension was reduced. The TFTs with dimensions smaller than 1.5 mu m showed transfer characteristics which were qualitatively different from those observed in the larger-dimension TFTs. In the TFT with W=L=0.5 mu m, the drain current changed from 50 pA to 15 mu A, corresponding to the gate voltage change of 40 mV. It is suggested that the observed switching phenomenon in the small-dimension TFTs may be related to avalanche-type breakdown at the grain boundary potential barrier, the height and width of which can be controlled by the gate voltage. >

Inosine Sensor Based on an Amorphous Silicon Isfet

Abstract A sensor for the determination of inosine was prepared by a combination of the enzyme system (shown below) and an amorphous silicon ISFET (a-ISFET). Nucleoside phosphorylase and xanthine oxidase were covalently immobilized on polyvinylbutyral membrane containing 1, 8-diamino-4-aminomethyloctane. The optimum conditions for determination of inosine were pH 7.5, 32[ddot] C. The sensor gave a linear relationship between the initial rate of the output gate voltage change and the logarithm of inosine concentration between 0.02 and 0.1 mM. Determination of inosine was possible within 7 min. The system could be used for two weeks with about 35% loss of enzymatic activity.

Magnetic field effects in strongly localized quasi-1D MOSFETs

We have measured the conductance as a function of gate voltage magnetic field, field orientation, and temperature of a quasi-1D silicon MOSFET in the strongly localized regime. At low temperatures and gate voltages, small changes in gate voltage produce large conductance fluctuations. The pattern of the fluctuations is changed dramatically as the magnetic field is increased, with some peaks vanishing and others growing out of the background. Much of the field dependence of the peak positions for different orientations and temperatures are due to Zeeman energy shifts.

Hypoxanthine sensor based on an amorphous silicon field-effect transistor

The pH response of an a-ISFET with xanthine oxidase immobilized on a ca. 20-μm thick poly(vinyl butyral) membrane over the gate insulator, is used to detect the uric acid produced by enzyme-catalyzed oxidation of hypoxanthine. The pH sensitivity between pH 5.0 and 10.0 is ca 48 mV/pH at 32°C in 10 mM phosphate buffer. The change in the output gate voltage 1 min after sample injection, is linearly related to the logarithm of the hypoxanthine concentration in the range 0.02–0.1 mM. The optimum buffer pH is 7.5. The system can be used for 2 weeks with 30% loss of enzymatic activity.

Back-gated field effect in a double heterostructure modulation-doped field-effect transistor

An Al/sub 0.3/Ga/sub 0.7/As/GaAs/Al/sub 0.3/Ga/sub 0.7/As double heterojunction field-effect transistor has been fabricated, the novel feature being a pn junction back gate. A device with 2 mu m channel length has yielded a change in transconductance by a factor of 2 for a change in back gate voltage of 1 V. The performance of this device shows that this approach could be used in realising novel devices, such as velocity modulation transistors. Also, the change in threshold voltage with back gate bias could be useful in implementing digital circuits.

A microsensor for urea based on an ion-selective field effect transistor

The pH response of a pH-sensitive field-effect transistor (FET) is not affected by a ca. 1-μm thick membrane formed from λ-aminopropyltriethoxysilane and glutaraldehyde over the gate insular by a vapor deposition method. The response between pH 5.5 and 8.5 is ca. 61 mV pH −1 at 37°C in 5 mM Tris-HCl buffer. When urease is immobilized on the membrane, the sensor gives a linear relationship between the initial rate of the output gate voltage change and the logarithmic value of urea concentration between 16.7 and 167 mM. Determination of urea is possible within 30 s. The optimum pH is 6.0–6.5, at 37°C. The system can be used for 20 days with only slight loss of enzymatic activity.

Review lecture: Metal–insulator transitions

A survey is given of a variety of solids that show a metal–insulator transition. In crystals most transitions are expected to be of first order as the composition or temperature is changed; in disordered systems this is not necessarily the case. The transition in an impurity band with change of donor concentration is described, and also with change of stress, magnetic field or gate voltage. The concept of a minimum metallic conductivity is discussed, with special reference to materials of mixed valence.