Showing papers on "Field-effect transistor published in 1986"

Macromolecular electronic device: Field-effect transistor with a polythiophene thin film

Abstract: The first solid‐state field‐effect transistor has been fabricated utilizing a film of an organic macromolecule, polythiophene, as a semiconductor. The device characteristics have been optimized by controlling the doping levels of the polymer. The device is a normally off type and the source (drain) current can be modulated by a factor of 102–103 by varying the gate voltage. The carrier mobility and the transconductance have also been determined to be ∼10−5 cm2/V s and 3 nS, respectively, by means of electrical measurements.

Simple technique for separating the effects of interface traps and trapped‐oxide charge in metal‐oxide‐semiconductor transistors

Abstract: A new technique is presented for separating the threshold‐voltage shift of a metal‐oxide‐semiconductor transistor into shifts due to interface traps and trapped‐oxide charge. This technique is applied to threshold‐voltage shifts on an n‐channel transistor that result from ionizing radiation.

One-Dimensional Conduction in the 2D Electron Gas of a GaAs-AlGaAs Heterojunction

Abstract: We present results on the transport properties of the 2D electron gas in a narrow channel formed by the split gate of a GaAs-AlGaAs heterojunction field-effect transistor. There are both quantum-interference and interaction corrections to the conductivity. We find that the temperature dependence of the phase relaxation length is in agreement with a recent theory based on scattering by electromagnetic fluctuations. Beyond the regime of quantum interference the conductivity varies with temperature as ${T}^{2}$.

Integrated semiconductor magnetic field sensors

Abstract: A magnetic field sensor is an entrance transducer that converts a magnetic field into an electronic signal. Semiconductor magnetic field sensors exploit the galvanomagnetic effects due to the Lorentz force on charge carriers. Integrated semiconductor, notably silicon, magnetic field sensors, are manufactured using integrated circuit technologies. Integrated sensors are being increasingly developed for a variety of applications in view of the advantage offered by the integration of the magnetic field sensitive element together with support and signal processing circuitry on the same semiconductor chip. The ultimate goal is to develop a broad range of inexpensive batch-fabricated high-performance sensors interfaced with the rapidly proliferating microprocessor. This review aims at the recent progress in integrated silicon magnetic devices such as integrated Hall plates, magnetic field-effect transistors, vertical and lateral bipolar magnetotransistors, magnetodiodes, and current-domain magnetometers. The current development of integrated magnetic field sensors based on III-V semiconductors is described as well. Bulk Hall-effect devices are also reviewed and serve to define terms of performance reference. Magnetic device modeling and the incorporation of magnetic devices into an integrated circuit offering in situ amplification and compensation of offset and temperature effects are further topics of this paper. Silicon will continue to be aggressively exploited in a variety of magnetic (and other) sensor applications, complementary to its traditional role as integrated circuit material.

A generalized theory of an electrolyte-insulator-semiconductor field-effect transistor

Abstract: A model of surface ionization and complexation of surface hydroxyl groups on the gate insulator surface is adapted in conjunction with electronic device physics to arrive at a generalized theory for the current-voltage characteristics of an electrolyte-insulator-semiconductor field-effect transistor (EISFET) in electrolyte solutions. EISFET's that employ thermally grown silicon dioxide were tested in simple electrolytes that contain Na+, K+, and Li+ions titrated in a p H range from 2 to 9. Experimental results show good agreement with the theory. The model successfully explains p H sensitivity, as well as the ion interference effect, of the EISFET working as a p H sensor. From this model, it is conluded that, among all the electrolyte parameters associated with an EISFET, the surface site density of the hydroxyl groups N s and the separation of surface ionization constants \Delta pK are the primary factors to consider when employing EISFET's as p H sensors. For high sensitivity and good selectivity, large N s and small \Delta pK values are required.

Subthreshold slope of thin-film SOI MOSFET's

Abstract: Silicon-on-insulator (SOI) n-channel transistors have been made in thin (90 nm) silicon films Both modeling and experimental results show that excellent subthreshold slopes can be obtained (62 mV/ decade) when the silicon film thickness is smaller than the maximum depletion depth in the transistor channel For comparison, the subthreshold slope of transistors made in thicker films is also reported

The delta-doped field-effect transistor (δFET)

Abstract: A field-effect transistor (FET) using a two-dimensional electron gas (2DEG) as an electron channel is fabricated from GaAs grown by molecular-beam epitaxy. The doping profile of the field-effect transistor is described by the Dirac delta (δ) function. The subband structure of δ-doped GaAs is calculated. The characteristics of the δFET are a high concentration of the 2DEG, a high breakdown voltage of the Schottky contact, a narrow distance of the 2DEG from the gate, and a high transconductance. These properties are analyzed. Preliminary results for the extrinsic transconductance and for the transit frequency are obtained from δFET's having nonoptimized structures.

Substrate hole current and oxide breakdown

Abstract: It is known that when an n‐channel metal‐oxide‐semiconductor field‐effect transistor is biased with a high positive gate voltage, a hole current appears in the substrate cathode. Recent experiments indicate that the holes are generated within the oxide. We show that this hole generation mechanism is linked to oxide time‐dependent breakdown. When the hole fluence reaches a certain critical value, breakdown occurs. This is in agreement with a hole‐trapping‐induced breakdown model. For very thin oxides the hole generation rate can become so low that the substrate hole current is dominated by the tunneling of valence‐band electrons which is not expected to contribute to oxide breakdown. A different mechanism of hole generation such as hot‐hole tunneling from the anode may be responsible for oxide breakdown in the important case of low gate voltage (<6 V).

Self‐consistent calculation of electron and hole inversion charges at silicon–silicon dioxide interfaces

Abstract: The charge distribution at a semiconductor‐insulator interface has been calculated, both for holes and electrons, by solving Schrodinger’s and Poisson’s equations self‐consistently for particles obeying Fermi–Dirac statistics. The results have been applied to carriers in the channel of a crystalline MOSFET (metal‐oxide‐semiconductor field‐effect transistor) with the (100) axis perpendicular to the gate oxide. For weak inversion, the self‐consistent results do not deviate significantly from those obtained assuming a triangular potential well, but for strong inversion the carriers tend to move closer to the oxide. The energy and occupation levels of the subbands are only affected by a few percent on passing from weak to strong inversion, keeping the transversal interface electric field fixed. Finally the gate capacitance has been calculated and found to agree with the experimental data published elsewhere.

The n-channel SiGe/Si modulation-doped field-effect transistor

Abstract: At the heterointerface of Si 1-x Ge x /Si the existence of two-dimensional carrier gas has recently been demonstrated. The electrons are confined inside the large-gap material Si. We report the first fabrication of n-channel modulation-doped SiGe/Si hetero field-effect transistors by use of molecular-beam epitaxial growth. Though neither layer sequence nor parasitic resistances were optimized, these first transistors exhibit an extrinsic transconductance of 40 mS/mm for a gate length of 1.6 µm. This value is higher than that of conventional Si MESFET's of comparable carrier concentration. Technological processing steps and device evaluation are described.

Low dark current GaAs metal-semiconductor-metal (MSM) photodiodes using WSi x contacts

Abstract: We present the fabrication and characterization of metal-semiconductor-metal (MSM) photodiodes using the same undoped GaAs layer that is used as a buffer layer in the epitaxial structure for GaAs field effect transistors (FET's). To study the dark current mechanism, various metal electrodes used for Schottky contacts are examined. A drastic V-shape relationship between the dark current of MSM photodiode and the Schottky barrier height is found. An extremely low dark current (a few nanoamperes) in the MSM photodiode is obtained by using tungsten silicide as electrode metal. It is concluded that the dark current is a function of a rivalry relation between the electron injection at the cathode and the hole injection at the anode. The internal gain of the MSM photodiode with tungsten silicide contacts is found, and possible mechanisms are discussed. A flat frequency response up to 1.3 GHz is obtained. The results shows the feasibility of MSM photodiodes for use as photodetectors with low minimum detectable power, and their applicability to monolithic integration with FET circuits.

Suspended gate field effect transistor modified with polypyrrole as alcohol sensor

Abstract: A generic type of new type of solid-state gas sensor is described that uses change of electron work function of a chemically sensitive layer in response to interaction with a gas or vapor. It is shown that if this layer is electrochemically deposited polypyrrole, the device responds to lower aliphatic alcohols. The new sensor operates at room temperature and has time response in seconds. 7 references, 8 figures, 1 table.

Enhancement- and depletion-mode p-channel Ge x Si 1-x modulation-doped FET's

Abstract: We report enhancement- and depletion-mode p-channel modulation-doped field-effect transistors (FET's) in Si. Si/Ge x Si 1-x heterostructures were grown by molecular-beam epitaxy (MBE) with one-dimensional confinement of holes at the heterostructure interfaces. Transconductances of 2.5 and 3.2 mS/mm were measured at 300 K for enhancement- and depletion-mode devices, respectively, in good agreement with transistor modeling predictions for p-channel devices using measured material parameters.

Inversion-layer capacitance and mobility of very thin gate-Oxide MOSFET's

Abstract: Inversion-layer capacitance has been experimentally characterized and identified to be the main cause of the second-order thickness-dependence of MOSFET characteristics. Field-dependent channel mobilities of both electrons and holes were independent of gate-oxide thicknesses from 50 to 450 A, e.g., there is no evidence of the alleged mobility degradation in very thin gate-oxide MOSFET's. Subthreshold slope, insignificantly affected by the inversion-layer capacitance, follows the simple theory down to ∼ 35 A of oxide thickness. The empirical equations for inversion-layer Capacitance and mobilities versus electric field are proposed.

Saturation of Threshold Voltage Shift in MOSFET's at High Total Dose

Abstract: We present the results of an investigation into the buildup of trapped positive oxide charge responsible for a negative component of radiation-induced threshold voltage shift in both hard and soft metaloxide semiconductor (MOS) gate oxides and the processes which limit this buildup. Hole-trapping effects at doses to 15 Mrad(SiO2) were examined in MOS field-effect transistors (MOSFET's) and MOS capacitors with 11- to 27-nm gate oxides. The observed saturation of threshold voltage shift was modeled with the aid of a computer simulation of charge buildup in an MOS structure and was found to be caused by a complex interaction between trap filling and recombination of radiation-generated free electrons with trapped holes, modulated by trapped-hole-induced distortion of the oxide electric field. A supplemental measurement of 10-keV x-ray-induced currents in MOS capacitors produced no evidence for radiation-generated hot electron injection from the Si substrate into SiO2 layers of various thicknesses and also yielded data on x-ray-induced charge generation in the SiO2.

Metastable defects in amorphous-silicon thin-film transistors.

Abstract: When a positive gate voltage is applied to an amorphous-silicon thin-film transistor, electrons become trapped in states close to the silicon-dielectric interface. This is studied by a new technique involving the transient discharge current produced under illumination. It is suggested that the behavior may involve metastable dangling bonds generated within the amorphous silicon as a consequence of the field-effect-induced increase in electron concentration. This constitutes an important new instability mechanism for amorphous-silicon thin-film transistors.

Microwave performance of a quarter-micrometer gate low-noise pseudomorphic InGaAs/AlGaAs modulation-doped field effect transistor

Abstract: We report excellent dc and millimeter-wave performance in In 0.15 Ga 0.85 As/Al 0.15 Ga 0.85 As pseudomorphic modulation-doped field effect transistors (MODFET's) with 0.25-µm-length gates. Extrinsic transconductances as high as 495 mS/mm at 300 K and unprecedented power performance in the 60-GHz range were observed. Although not yet optimized, excellent low noise characteristics, 0.9 dB, with an associated gain of 10.4 dB at 18 GHz, and a noise figure of 2.4 dB with an associated gain of 4.4 dB at 62 GHz were obtained. This is the best noise performance ever reported for a MODFET in this frequency range. These results clearly demonstrate the superiority of pseudomorphic MODFET structures in high-frequency applications.

Semiconductor device with protective means against overheating

Abstract: A semiconductor substrate has a power region and a control region. The control region is located in the center portion of the substrate, and the power region surrounds the control region and is separated therefrom. A vertical type, MOS transistor, i.e., an active semiconductor element, is formed on the power region. An insulation film is formed on part of the control region. A polycrystalline silicon diode, which functions as a heat-sensitive element, is formed on the insulation film. A control section comprising a lateral type, MOS transistor is also formed on the control region. The lateral type, MOS transistor is connected to receive a signal form the polycrystalline silicon diode. Further, a polycrystalline silicon resistor, which determines a circuit constant, is formed on the insulation film. The MOS transistor protects the active semiconductor element in response to a signal supplied from the heat-sensitive element showing that the temperature of the semiconductor substrate has risen above a predetermined value. For example, the active semiconductor element may be disabled until the detected temperature drops below a predetermined value.

Static and dynamic analysis of amorphous-silicon field-effect transistors

Abstract: Analytical expressions have been developed for the analysis of static and dynamic behaviour of hydrogenated-amorphous-silicon based field-effect transistors. The current/voltage, capacitances and transcapacitances/voltage characteristics are related to the material parameters. The characteristic temperature, Tc, of the exponential band-tail states distribution is shown to influence strongly their shape and magnitude. An exact integration of the potential in the structure has allowed us to give expressions for the source and drain resistances. Finally, we present an equivalent circuit of a-Si:H TFT which can be employed in circuit simulation for the optimisation of integrated circuits.

Forming memory transistors with varying gate oxide thicknesses

Abstract: A semiconductor integrated circuit device and a method of manufacturing the same, wherein an MIS type memory transistor of a two-layered gate electrode structure is formed on the surface of a semiconductor substrate, and an MIS type transistor for a low voltage having a comparatively thin gate oxide film and an MIS type transistor for a high voltage having a comparatively thick gate oxide film are formed around the memory transistor.

On the low-temperature degradation of (AlGa)As/GaAs modulation-doped field-effect transistors

Abstract: A comprehensive study of the anomalous low-temperature behavior of modulation,doped (Al, Ga)As/GaAs field-effect transistors is reported, Experiments on the effect of bias stress on the current-voltage characteristics in lateral resistors, 1-µm gate FET's, and a novel dual-gate tester are presented along with the results of freeze-out, optical spectroscopy, and trapping kinetics experiments. Both modulation-doped (Al, Ga)As/GaAs heterostructures and isolated (Al, Ga)As layers are examined. The results delineate the conditions under which threshold shift and I-V collapse occur. Based on these results a detailed physical model which explains these effects is proposed. One important conclusion of this work is that the collapse is not related to hot electron injection from the high mobility channel, as suggested earlier, but is a property of a highly doped AlGaAs layer under bias.

Modulation-doped GaAs/(Al,Ga)As heterojunction field-effect transistors: MODFETs

Abstract: Recently developed modulation-doped field-effect transistors (MODFETs) now hold the record for high-speed logic. In this device structure only the larger bandgap (Al,Ga)As layer is doped with donors and the GaAs layer is left undoped. Electrons minimize their energy by diffusing out of the (Al,Ga)As into the lower potential GaAs where they form a two-dimensional electron gas near the heterointerface. Since the electrons and donors are spatially separated, ionized impurity scattering is avoided making it possible to obtain extremely high electron mobilities. Even at electron densities of 1019cm-3or ∼ 1 × 1012cm-2per interface, transport properties of these heterostructures are comparable to pure bulk GaAs. Modulation-doped FETs using this heterojunction system offer many advantages among which are a small gate to conducting channel separation (∼ 300 A) leading to extremely high transconductances, a large current-carrying capability (∼ 500 mA/mm per interface), a small source resistance, and a small saturation voltage. The benefits improve quite substantially at 77 K where the transconductance increases to ∼ 500 mS/mm. Improved device performance has been obtained in both high-speed and digital applications. Modulation-doped FETs used as low-noise amplifiers exhibit noise figures as low as 0.4 dB with 14-dB gain at 10 GHz at 77 K and a noise temperature of 3.5 K at 3.3 GHz with the MODFET cooled to 15 K. The rate of increase in noise temperature is about 1 K/GHz. Quarter micrometer devices have exhibited a current-gain cutoff frequency of 70 GHz. When used as inverters in logic circuits, propagation delays of 12 ps and under 10 ps have been obtained at 300 and 77 K, respectively. Delay times as low as 5 ps are quite possible at 77 K. Static RAMs with 4-kbit complexity exhibited access times of about 2 ns. These results are far superior to any other three-terminal device which is the primary reason why numerous university, industrial, and government laboratories in the U.S., Europe, and Japan have sizable MODFET programs.

Method of making a thin film transistor with laser recrystallized source and drain

Abstract: A method of manufacturing an insulated gate field effect transistor by forming a non-single crystalline semiconductor film of a first conductivity type on an insulating substrate where the semiconductor film includes hydrogen or fluoride, forming a gate insulating film on part of the semiconductor film to be the gate region, forming a gate electrode on the insulating film, inverting the conductivity type of the part of the conductor film to be the source and grain regions by ion doping of impurity corresponding to the second conductivity type opposite to the first conductivity type with the gate electrode functioning as a mask, and then exposing the non-single-crystalline semiconductor film to illumination with the gate electrode functioning as a mask to selectively crystallize the source and drain regions.

Study of the quasi-saturation effect in VDMOS transistors

Abstract: The quasi-saturation effect in VDMOS transistors is studied in detail. It is shown that such behavior is due to carrier velocity saturation in the JFET region of the device. Two-dimensional numerical simulation is carried out to study the quasi-saturation effect and its relation to different device design parameters. Experimental results over a wide range of voltage and current levels are used to verify calculated dc characteristics. In addition, the design constraint on p-body spacing in order to avoid the quasi-saturation effect is defined.

A MODFET dc model with improved pinchoff and saturation characteristics

Abstract: We present an analytical dc model for the MODFET that offers several improvements over existing models. An enhanced version of the model makes use of a new approximation of the two-dimensional electron gas (2DEG) concentration versus gate-to-channel voltage, which models both the subthreshold region and the gradual saturation of carriers due to the onset of AlGaAs charge modulation. Even in this more accurate model there are no complicated numerical calculations involved; at most what is required is finding a single root of a function of one variable. We propose an electron velocity-field curve that combines the observed field-dependent mobility in the 2DEG, and the sharp velocity saturation in GaAs. We use a two-region Grebene-Ghandhi model with floating boundary for the channel. The quasi-linear region on the source side is treated by the gradual channel approximation and extends toward the drain up to a point where the field reaches its threshold for velocity saturation. Between this point and the drain-side end of the channel, the potential is determined by the two-dimensional Poisson equation in the AlGaAs region. The resuiting I-V characteristics and their slopes are continuous. The model predicts a maximum transconductance and a finite intrinsic output conductance in the saturated region, two features experimentally observed but not predicted by previous models. In the limit of very short gate lengths the model approaches the saturated velocity model, while in the limit of very long gate lengths it approaches the classical gradual channel model.

Thin film FET doped with diffusion inhibitor

Abstract: The present invention relates to a semiconductor device including a MOS transistor which is formed with a source region, a drain region and a channel region by the use of polycrystalline silicon, and a method of manufacturing the semiconductor device. Ions of carbon, oxygen or/and nitrogen are introduced into a polycrystalline silicon layer over the whole area thereof, and restrain conductive ions in the source and drain regions from diffusing into the channel region.

SiO2‐induced substrate current and its relation to positive charge in field‐effect transistors

Abstract: Experimental data are presented for the substrate current (holes), which accompanies electron injection into the oxide of n‐channel field‐effect transistor structures, in the tunneling regime. Dependencies of the effect on oxide thickness and on the metal gate material were investigated. An inverse relation was found between the initial rise time of oxide current transients and both the electron and hole currents. It is shown that these initial current increases are related to positive charge, therefore a correlation exists between the positive charge and electron or hole currents. The strength of impact ionization in SiO2 is discussed on the basis of band‐structure arguments and it is concluded that there are difficulties in explaining the substrate current by impact ionization. A technique for fast measurements of capacitance‐voltage shifts at the end of an applied high field pulse is described.

Improved subthreshold characteristics of n-channel SOI transistors

Abstract: It has been found that certain n-channel MOSFET's fabricated on silicon-on-insulator (SOI) substrates formed by oxygen implantation can have \log (I_{d}): V_{gs} , characteristics with very steep slopes in the subthreshold region. In contradiction to normal models for short-channel transistors on bulk silicon, the slope becomes steeper for shorter gate lengths or higher drain voltages. This effect is shown to be related to the kink in the output characteristics of transistors with floating islands.

Chemical-sensitive semiconductor device

Abstract: A chemical-sensitive semiconductor device in the form of a chemical-sensitive field effect transistor, suitable for testing relatively small volumes of a fluid analyte, comprises a substrate provided with a passageway, interconnecting its major surfaces, along which the analyte can pass. Drain and source regions are formed at opposite ends of the passageway and a chemical-sensitive gate region is formed on the sides of the passageway.