FET Source Research Articles

Evidence of contact-induced variability in industrially-fabricated highly-scaled MoS2 FETs

Evidence of microscopic inhomogeneities of the side source/drain contacts in 300 mm wafer integrated MoS2 field-effect transistors is presented. In particular, the presence of a limited number of low Schottky barrier spots through which channel carriers are predominantly injected is demonstrated by the dramatic current changes induced by individual charge traps located near the source contact. Two distinct types of “contact-impacting traps” are identified. Type-1 trap is adjacent to the contact interface and exchanges carriers with the metal. Its impact is only observable when the adjacent contact is the reverse-biased FET source and limits the channel current. Type-2 trap is located in the AlOx gate oxide interlayer, near the source contact, and exchanges carriers with the channel. Its capture/emission time constants exhibit both a gate and drain bias dependence due to the high sensitivity of the contact regions to the applied lateral and vertical fields. Unlike typical channel-impacting oxide traps, both types of reported defects affect the Schottky barrier height and width rather than the threshold voltage and result in giant random telegraph noise (RTN). These observations indicate that the contact quality and geometry play a fundamental role in the ultimate scaling of 2D FETs.

Phase- and Angle-Sensitive Terahertz Hot-Electron Bolometric Plasmonic Detectors Based on Fets with Graphene Channel and Composite H-BN/Black-P/H-BN Gate Layer

In this paper, we propose and analyze the terahertz (THz) bolometric vector detectors based on the graphene-channel field-effect transistors (GC-FET) with the black-P gate barrier layer or with the composite b-BN/black-P/b-BN gate layer. The phase difference between the signal received by the FET source and drain substantially affects the plasmonic resonances. This results in a resonant variation of the detector response on the incoming THz signal phase shift and the THz radiation angle of incidence.

Comparison study of RF/analog and linearity performance of dual material gate graphene source vertical TFET (DMG-GR-VTFET) and single material gate GR-VTFET

This paper investigates the comparative feature of Graphene Source Single Material Gate Vertical Tunnel FET (SMG-GR-VTFET) and Graphene Source Double Material Gate VTFET (DMG-GR-VTFET) on DC, analog/RF and linearity applications using Sentaurus TCAD simulator. The results show that both devices outperforms in DC characteristics, including ambipolar current, subthreshold swing (SS), ION/IOFF ratio etc The study focuses on important figures of merit (FOMs) such as transconductance (gm), output conductance (gd), cut-off frequency (ft), second-order transconductance (gm2), third-order transconductance (gm3), VIP2, and VIP3, which are all improved due to high mobility of graphene leads to improved band-to-band tunneling. The observed ION is 5.2 × 10−4 (1.1 × 10−3 A/μm), IOFF is 1.439 × 10−13 (2.28 × 10−16A/μm) and ION/IOFF ratio of 3.613 × 109 (4.824 × 1012) for SMG-GR-VTFET (DMG-GR-VTFET), respectively. It is seen that maximum gm is 2.96 × 10−3 (2.59 × 10−3 S μm−1) and cut-off frequency (ft) values of 1.1 × 1011 (1.85 × 1011 Hz) for SMG-GR-VTFET (DMG-GR-VTFET), respectively. Regarding the Linearity parameter VIP2 value is 2.71 V (0.99 V), respectively, for SMG-GR-VTFET (DMG-GR-VTFET). These results suggest that Graphene Source Vertical Tunnel FET is an excellent choice for analog and high-frequency applications.

Band-like transport observed in TIPS-pentacene thin film by time-resolved microscopic optical second-harmonic generation imaging

Carrier transport in single-crystalline grains of 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene was studied using time-resolved microscopic optical second-harmonic generation (TRM-SHG). TRM-SHG is used to directly visualize carrier injection and transport behavior in TIPS pentacene. A strong SHG signal observed at the edge of a FET source electrode at low temperature suggests the presence of a potential drop associated with the carrier injection process. An accurate carrier mobility calculation, taking into account the potential drop, shows a negative slope with temperature that indicates band-like transport.

Steep-slope nanowire FET with a superlattice in the source extension

In this work we report the main results of a research activity on a novel device concept which aims to achieve a steep switching behavior based on the filtering of high-energy electrons in the FET source region. The filtering function is entrusted to a superlattice in the source extension, which could possibly be fabricated by depositing a number of appropriate semiconductor layers within the manufacturing process of vertical nanowires. Simulation results indicate that a sustained inverse switching slope SS=26mV/dec can be achieved using GaAs/AlGaAs as the constituent materials of the superlattice, and that an on-current ION=0.5mA/μm can be obtained at VGS=VDS=0.4V by a careful optimization of the superlattice geometry. Further improvements are expected by an appropriate choice of the semiconductor pairs.

Internal noise in miniature electret microphones

Modern miniature electret microphones normally include an internal amplifier to buffer the very high electrical impedance of the electret motor. This amplifier, usually an FET source follower circuit, generates a part of the noise in the microphone output signal. The electrical noise originates in the semiconductor and in the resistive components of the electrical circuit. Recent developments have reduced the electrical noise considerably so that it is no longer the dominant source. The other noise sources are the resistive components of the mechanical and acoustical impedances within the microphone. This paper describes recent work and special measurement methods that have helped to identify and reduce the acoustical noise components.

Device characteristics and its operation mechanism of a FET-type waveguide modulator using α-sexithienyl

An optical waveguide modulator having a field-effect transistor-type electrode using a thiophene oligomer, α-sexithienyl (6T), has been fabricated and has functioned as an electro-absorption modulator with the modulation ratio of 20%. The optical modulation is directly related with the FET device operation, and has shown a maximum at 830 nm for propagating light wavelength. Therefore, the mechanism of the optical modulation has been clarified to be the increasing absorption due to polarons induced by negative bias. The linear relationship between the modulation ratios and the FET source currents has led to the conclusion that the polaron conversion efficiency η was introduced as the new parameter to understand the device operation, which has become clear. From the analysis, the nearly intrinsic value of carrier mobility of 6T was extrapolated, and the limit of the improving the carrier mobility was also shown. The possibility of enlarging the modulation ratio and its frequency dependence is also discussed.

Active radiating oscillator using a reflection amplifier module

A new radiating oscillator module is presented in which the cavity consists of an FET source and a multilayer slot coupled patch antenna exhibiting either an oscillator or an antenna. Oscillation conditions and design criteria of the structure are studied. Prototype circuits showed 4.81 mW power output and 50 MHz tuning range at 4.893 GHz.

Pyroelectric detectors and their applications

The authors review the principles of operation of pyroelectric detectors. The equations for current responsivity, voltage responsivity, noise, noise equivalent power, and detectivity are derived from the fundamental thermodynamic model of a pyroelectric detector. The frequency-dependent current and voltage responsivities are explained. Factors influencing the choice of pyroelectric material for various applications are summarized. The possibilities of various new applications and the developments of pyroelectric detectors are discussed. A laboratory prototype demonstration system has been built using an ELTEC detector type 5192. For a high signal-to-noise ratio, an electric charge integration technique is applied. High-precision operational amplifiers are used for high-quality signal conditioning. The pyroelectric detector consists of two parallel opposed dual lithium tantalate pyroelectric single crystals with a junction FET source follower sealed in a standard TO-5 housing. >

Performance of a silicon mustrip detector with a new type of preamplifier for nuclear experiments

For tracking secondary beam particles, we developed a silicon mustrip detector (400 μm strip width and 500 μm strip pitch) with an unconventional type of preamplifier which consists of an FET source follower at the input stage and an operational amplifier at the following stage. Some kinds of FETs were tested as input stage devices. The size of the preamplifier is 4.5×4.5 cm 2 with 4 channels. We achieved an energy resolution of 12 keV (FWHM) with a fall time of 500 ns which was sufficient to detect minimum-ionizing particles such as 1.5 GeV/ c pions or 4 GeV/ c protons.

A new piezoelectric microphone with divided electrodes

A new type of piezoelectric ceramic microphone is proposed. Its merits are as follows. (1) High output, high efficiency—A high output voltage was obtained by dividing the piezoelectric ceramic electrodes and connecting them in series. The output voltge is proportional to the number of divisions. However, since the impedance is high, an FET circuit is required to decrease output impedance. At the same time, an improvement of the signal-to-noise ratio was also realized. (2) Reduction of diaphragm mechanical impedance—To improve the matching to the impedance of air, a mechanical transformer was introduced. The center of the diaphragm was lightened and its rigidity was increased by combining a dome-type diaphragm and ring-shaped piezoelectric ceramic. This made it easy to control the frequency response. (3) Stability—The diaphragm consists of a Y2O3⋅PSZ ceramic thin film formed into a dome shape and laminated to a ring-shaped ceramic. This structure showed a higher temperature stability and noticeably lower aging change than the conventional flat-type diaphragm. The specifications of the prototype microphone are the following: diameter, 1 in. (23.8 mm), nondirectional; sensitivity, −59 dB/uμbar at FET source output; frequency response, 20 Hz–12.5 kHz −+ 1.5 dB; S/N ratio, 59 dB A-weighted.

X-band varactor tuned monolithic GaAs FET oscillators†

Abstract The design, fabrication and performance of X-band varactor-tuned monolithic GaAs FET oscillators is described. The design is based on small and large signal device characteristics. A manufacturable process is used in order to realize the oscillators. The experimental performance agrees with the theoretical expectations within 0·2% for the oscillation frequency and 4% for the tuning bandwidth. Best tuning bandwidth and output power values exceeded 2 GHz and 28 mW. Wafer dispersion depends on oscillator characteristics and varies between ±1% and ±7·7% for oscillators with a varactor in the FET source. The rf wafer yield is 65%. Finally, noise and temperature characteristics are given.

Active radiating element using FET source integrated with microstrip patch antenna

An FET source has been integrated with a microstrip patch antenna to form an active radiating module. The patch antenna serves both as a radiating element and a resonator in the feedback loop for the FET oscillator. Power output of 17mW was achieved at 5.7 GHz.

FET Characterization using gated-TLM structure

A new FET characterization structure consisting of parallel ohmic contacts with gates of varying lengths in between is described. The FET source resistance is accurately measured without parameter fitting or iteration. The low-field electron mobility beneath the gate is determined as an effective uniform value and as a function of distance into the channel without iteration. The use of this structure is demonstrated on self-aligned ion-implanted GaAs MESFET's.

Self-Consistent GaAs FET Models for Amplifier Design and Device Diagnostics

A procedure has been developed for producing accurate and unique small-signal equivalent circuit models for carrier-mounted GaAs FET's. The procedure utilizes zero drain-source bias S parmeter tests to determine accurate values of carrier parasitics, and dc measurements to evaluate the FET's gate, source, and drain resistances. Subsequent S-parameter measurements at full bias are then used to resolve the FET into an equivalent circuit model that has only 8 unknown elements out of a possible 16. A technique for evaluating the frequency range of accurate data is presented and the FET model shown is useful well above the maximum frequency of measurement. Examples of device diagnostics are presented for RCA flip-chip mounted GaAs FET's.

Photoelectrochemical plating of via GaAs FET's

A new photoelectrochemical (PEC) technique for filling via holes in GaAs FET's with a solid deposit of metal, such as gold, has been developed. Photogenerated electrons reduce solvated Au(CN) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -, directly on the FET source pads, allowing narrow straight-walled plasma-etched via holes to be filled without forming voids. The photogenerated holes cause the decomposition of a small amount of the semi-insulating (SI) substrate. With illumination from a 1200-W tungsten-halogen lamp, plating rates of 0.8 µm/min over a 2-in-diam wafer are achieved. The plating rate is insensitive to Au(CN) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> - concentration in the range 0.01 to 0.15 M. The resulting GaAs FET's show improved mechanical stability and thermal resistance.

Self-aligned submicron gate digital GaAs integrated circuits

Digital normally-off (ENFET) GaAs integrated circuits have been fabricated using a novel self-aligned gate process that has produced high speed ring-oscillators with propagation delays as low as 25 ps and other low power circuits with power dissipation as small as 16 µW (at room temperature). The process is unique in that it permits control of parasitic FET source resistance and gate capacitance and also can achieve submicron gate lengths using conventional optical lithography.

A Technique for Measuring Extremely Low Ionization Chamber Currents Using MOS FET Circuitpry

A circuit has been developed for an Isotope Calibrator which will accurately measure ionization chamber currents in the order of 10-14 to 10-7amps. The circuit incorporates a self-zeroing feedback network which virtually eliminates drift, as well as high impedance MOS FET switches and a MOS insulated gate FET source follower in the input circuit to minimize errors due to leakage currents.

Insulated Active Electrodes

The need for reliable, easily applied, dry electrodes for use in medical applications has prompted investigation in many directions. Most wet or paste type electrodes are not only irritating to the skin when used over long periods of time, but also require careful skin preparation for clinically useful results. An insulated electrode technique has been reported which requires no skin preparation and is immune to artifacts induced by electrode polarization. This electrode consists of an anodized metal disc which relies upon capacitive coupling with the skin to derive its electrical signal. The signal output of the electrode is coupled directly into an FET source follower which has an output impedance of 5000 ohms, and is coupled into standard clinical recording equipment. This paper reports further improvements in the development of electrodes of this type.

Measurement of High Q at High Frequencies

A high Q tuned circuit is shock excited by the pulsed interruption of current flow through a pair of charge-storage diodes. The resulting damped oscillation is recorded via an FET source follower on a CRO or X-Y recorder. The Q is calculated from the observed logarithmic decay period. A Q of over 900 is readily measured at 60 MHz. The method is useful in the measurement of varactor series resistance and in the checking of the loading imposed by other components. The accuracy of the method is also discussed.