P-channel Mode Research Articles

Temperature-Dependent Feedback Operations of Triple-Gate Field-Effect Transistors.

In this study, we examine the electrical characteristics of triple-gate feedback field-effect transistors (TG FBFETs) over a temperature range of -200 °C to 280 °C. With increasing temperature from 25 °C to 280 °C, the thermally generated charge carriers increase in the channel regions such that a positive feedback loop forms rapidly. Thus, the latch-up voltage shifts from -1.01 V (1.34 V) to -11.01 V (10.45 V) in the n-channel (p-channel) mode. In contrast, with decreasing temperature from 25 °C to -200 °C, the thermally generated charge carriers decrease, causing a shift in the latch-up voltage in the opposite direction to that of the increasing temperature case. Despite the shift in the latch-up voltage, the TG FBFETs exhibit ideal switching characteristics, with subthreshold swings of 6.6 mV/dec and 7.2 mV/dec for the n-channel and p-channel modes, respectively. Moreover, the memory window widens with increasing temperature. Specifically, at temperatures above 85 °C, the memory windows are wider than 3.05 V and 1.42 V for the n-channel and p-channel modes, respectively.

Logic and memory functions of an inverter comprising reconfigurable double gated feedback field effect transistors

In this study, we propose an inverter consisting of reconfigurable double-gated (DG) feedback field-effect transistors (FBFETs) and examine its logic and memory operations through a mixed-mode technology computer-aided design simulation. The DG FBFETs can be reconfigured to n- or p-channel modes, and these modes exhibit an on/off current ratio of ~ 1012 and a subthreshold swing (SS) of ~ 0.4 mV/dec. Our study suggests the solution to the output voltage loss, a common problem in FBFET-based inverters; the proposed inverter exhibits the same output logic voltage as the supply voltage in gigahertz frequencies by applying a reset operation between the logic operations. The inverter retains the output logic ‘1’ and ‘0’ states for ~ 21 s without the supply voltage. The proposed inverter demonstrates the promising potential for logic-in-memory application.

Reconfigurable Artificial Synapses with Excitatory and Inhibitory Response Enabled by an Ambipolar Oxide Thin-Film Transistor.

A gate-tunable synaptic device controlling dynamically reconfigurable excitatory and inhibitory synaptic responses, which can emulate the fundamental synaptic responses for developing diverse functionalities of the biological nervous system, was developed using ambipolar oxide semiconductor thin-film transistors (TFTs). Since the balanced ambipolarity is significant, a boron-incorporated SnO (SnO:B) oxide semiconductor channel was newly developed to improve the ambipolar charge transports by reducing the subgap defect density, which was reduced to less than 1017 cm-3. The ambipolar SnO:B-TFT could be fabricated with a good reproductivity at the maximum process temperature of 250 °C and exhibited good TFT performances, such as a nearly zero switching voltage, the saturation mobility of ∼1.3 cm2 V-1 s-1, s-value of ∼1.1 V decade-1, and an on/off-current ratio of ∼8 × 103 for the p-channel mode, while ∼0.14 cm2 V-1 s-1, ∼2.2 V decade-1and ∼1 × 103 for n-channel modes, respectively. The ambipolar device imitated potentiation/depression behaviors in both excitatory and inhibitory synaptic responses by using the p- and n-channel transports by tuning a gate bias. The low-power consumptions of <20 and <2 nJ per pulse for the excitatory and inhibitory operations, respectively, were also achieved. The presented device operated under an ambient atmosphere and confirmed a good operation reliability over 5000 pulses and a long-term air environmental stability. The study presents the high potential of an ambipolar oxide-TFT-based synaptic device with a good manufacturability to develop emerging neuromorphic perception and computing hardware for next-generation artificial intelligence systems.

Temperature-Dependent Electrical Characteristics of p-Channel Mode Feedback Field-Effect Transistors

In this study, the temperature-dependent electrical characteristics of p-channel mode feedback field-effect transistors (FBFETs) were examined at temperatures ranging from 250 to 425 K. Their steep subthreshold swings of less than 1 mV/dec were maintained even at temperatures up to 400 K. As the temperature increased to 400 K, the latch-up voltage shifted from -0.951 to -0.613 V, which was caused by a reduction in the potential barriers in the channels of the FBFETs. High Ion/Ioff ratios above 108 were maintained in the temperature range of 250 to 400 K. However, at temperatures over 400 K, the FBFETs were turned on regardless of the gate voltages owing to the generation of a thermally induced positive feedback loop.

Ambipolar Gas Sensing Behaviors for Collection of Two-Dimensional Data from a Single Device

An electronic nose (e-nose), an array of different individual chemiresistive sensors, has been proposed to mimic olfaction system of mammals. The e-nose provides a unique pattern for each gas species, which enables one to distinguish gases and their concentrations. Therefore, it demands as much reliable data as possible to improve gas selectivity. Increasing the number of constituting sensors allows to collect massive data, thus gives more chances to reduce errors, but this suffers from the complex and high-cost fabrication. More economical solution is collecting highly-distinguishable data from each sensor, which can produce more reliable results with reduced errors. In this presentation, we propose a new concept of collecting two-dimensional response data by making a single device show ambipolar sensing behaviors, thus, both p-type (the resistance increases in oxidative gases) and n-type (the resistance decreases in oxidative gases) sensing behaviors. The proposed concept utilizes the response direction (sign of the gas response) as well as the response amplitude, differentiated from other methods that produces monotonous data from each sensor by reading only the response amplitude.Firstly, we have demonstrated the ambipolar gas sensing behaviors in diode-type device; p-type NiO/n-type SnO2 diode, and NiO/Ti/Au Schottky diode. The ambipolar behavior is attributed to the predominant modulation of heterojunction barrier. Our unique device architecture has a single well-defined heterojunction formed by vertically aligned nanostructures and electrodes in a top-bottom configuration, facilitating the heterojunction barrier modulation. We also show the ambipolar sensing behavior in an organic thin-film transistor (OTFT)-based gas sensor that can operate in both n-channel and p-channel modes depending on the gate bias. Indeed the ambipolar OTFT-based gas sensor produces two-dimensional data depending on the gate biases. Our result reveal that the proposed ambipolar sensing concept allows the collection of two-dimensional data from a single device in a reliable manner, which can significantly contribute to enhance gas selectivity of e-nose.

Demonstration of a GaN/AlGaN Superlattice-Based p-Channel FinFET With High ON-Current

In this letter, we report on the demonstration of a Mg-doped GaN/Al0.2Ga0.8N superlattice (SL) based depletion mode p-channel FinFET to improve the on current (ION). A two-step approach involving a dry etch followed by a Tetramethylammonium hydroxide (TMAH) wet etch was employed to obtain fins with minimum width of 50 nm using optical lithography. Normalizing current with fin height, an ION of 52 mA/mm and 110 mA/mm were achieved for 80 and 105 nm wide fins respectively.

Steep Subthreshold Swing n- and p-Channel Operation of Bendable Feedback Field-Effect Transistors with p(+)-i-n(+) Nanowires by Dual-Top-Gate Voltage Modulation.

In this study, we present the steep switching characteristics of bendable feedback field-effect transistors (FBFETs) consisting of p(+)-i-n(+) Si nanowires (NWs) and dual-top-gate structures. As a result of a positive feedback loop in the intrinsic channel region, our FBFET features the outstanding switching characteristics of an on/off current ratio of approximately 10(6), and point subthreshold swings (SSs) of 18-19 mV/dec in the n-channel operation mode and of 10-23 mV/dec in the p-channel operation mode. Not only can these devices operate in n- or p-channel modes, their switching characteristics can also be modulated by adjusting the gate biases. Moreover, the device maintains its steep SS characteristics, even when the substrate is bent. This study demonstrates the promising potential of bendable NW FBFETs for use as low-power components in integrated circuits or memory devices.

Enhancement mode p-channel SnO thin-film transistors with dual-gate structures

The authors demonstrate the enhancement mode p-type SnO thin-film transistors (TFTs) using dual gate (DG) structures. The cross-linked polyvinyl alcohol dielectric with a polymethylmethacrylate buffer layer is formed as a top gate (TG) insulator of the DG SnO TFT. The fabricated DG SnO TFT exhibits better electrical performances than the bottom gate (BG) and TG SnO TFTs including higher field-effect mobility and smaller subthreshold slope. In fabricated DG TFTs, the threshold voltage (Vth) of the BG TFT is linearly modulated by the voltage applied to the TG electrode. The BG transfer curve exhibits a depletion mode operation when measured while TG is grounded, but operates in the enhancement mode with a negative Vth (=−0.9 V) when a positive bias of 10 V is applied to the TG electrode. The enhancement mode operation of p-type SnO TFTs can increase the output voltage swing range and decreases the off-stage leakage currents of the complementary logic circuits.

Tuning the Ge(Sn) Tunneling FET: Influence of Drain Doping, Short Channel, and Sn Content

We present experimental results on the realization of p-channel mode Ge(Sn) heterojunction band-to-band tunneling field effect transistors. We investigate the influence of three device parameters (drain doping, channel length, and tunnel barrier height at source side) of the semiconductor body of the devices on the device performance. We achieve a complete suppression of the n-channel mode in p-type operating conditions by systematically reducing the p-type drain doping from 1·10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> to 2 · 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , examined in sample series A. In the second sample series B, we investigate the influence of a reduction of the channel length down to 15 nm on transistor performance. To improve the ON current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> without degrading the OFF current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> , we introduce a 10-nm delta layer of a Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> alloy at the source/channel junction in the third sample series C. We demonstrate an improved ON current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> compared with the reference sample without a GeSn delta layer.

P-Channel Enhancement and Depletion Mode GaN-Based HFETs With Quaternary Backbarriers

Within the last years, III-nitride-based devices have been demonstrated with exceptional performance. There is, however, a severe lack of knowledge when it comes fabrication of p-channel devices. p-Channel heterostructure field-effect transistors (HFETs) could open the way for nitride-based complementary logic. Here, a comprehensive study of enhancement and depletion mode p-channel GaN/AlInGaN HFETs is performed. The influence of a highly p-doped GaN cap layer on device performance is investigated. Gate recessing and changes in composition of the backbarrier are analyzed. ON/OFF ratios of up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> and subthreshold swings of about 75 mV/decade are achieved.

An analytical model for bio-electronic organic field-effect transistor sensors

A model for the electrical characteristics of Functional-Bio-Interlayer Organic Field-Effect Transistors (FBI-OFETs) electronic sensors is here proposed. Specifically, the output current-voltage characteristics of a streptavidin (SA) embedding FBI-OFET are modeled by means of the analytical equations of an enhancement mode p-channel OFET modified according to an ad hoc designed equivalent circuit that is also independently simulated with pspice. An excellent agreement between the model and the experimental current-voltage output characteristics has been found upon exposure to 5 nM of biotin. A good agreement is also found with the SA OFET parameters graphically extracted from the device transfer I-V curves.

Dynamic analytical model for charge transport in octithiophene thin film transistors

In this paper, we develop a device model of an organic thin film transistor (OTFTs) in which the active layers are made of octithiophene. This model is based on variable range hopping theory, i.e., a carrier may either hop over a small distance with a high activation energy or hop over a long distance with a low activation energy. The model takes into account all the operating regimes in direct current and transient mode; the transistor symmetry is also considered. The model has been developed using a physical basis where the model parameters can easily be extracted. The current–voltage characteristics of short-channel organic TFTs have been calculated starting from the solution of the drain current equation for an enhancement mode p-channel MOSFET. A good agreement between theory model and experimental results is obtained. Different transport parameters are extracted by using a fitting method. We have extracted the mobility of charge in saturation regime using differential method. Based on first and second derivative of transfer characteristic we extracted a serial resistance, intrinsic mobility and threshold voltage. The mobility in saturation regime is reproduced using the VRH model. Finally, we give a simple small-signal equivalent circuit.

Drain breakdown voltage: A comparison between junctionless and inversion mode p-channel MOSFETs

A comparative study of the drain breakdown phenomena in junctionless (JL) and inversion mode (IM) p-channel MOSFETs has been investigated experimentally with different VGS, channel widths, and VSUB. In order to explain the dependence of drain breakdown voltages (BVDS) on VGS, 3-D device simulation has been also performed. When the device is turned ON, the BVDS is larger in JL than IM transistors. The BVDS is decreased with the increase of |VGS| in IM transistors but it is increased in JL transistors. When the device is turned OFF, the BVDS is larger in IM than JL transistors. The BVDS is decreased with the increase of channel width for JL and IM transistors. The BVDS is decreased in IM transistor when the back surface state of Si film is changed from the accumulation to the inversion but it is almost constant in JL transistors.

Bias-Stress Effect in 1,2-Ethanedithiol-Treated PbS Quantum Dot Field-Effect Transistors

We investigate the bias-stress effect in field-effect transistors (FETs) consisting of 1,2-ethanedithiol-treated PbS quantum dot (QD) films as charge transport layers in a top-gated configuration. The FETs exhibit ambipolar operation with typical mobilities on the order of μ(e) = 8 × 10(-3) cm(2) V(-1) s(-1) in n-channel operation and μ(h) = 1 × 10(-3) cm(2) V(-1) s(-1) in p-channel operation. When the FET is turned on in n-channel or p-channel mode, the established drain-source current rapidly decreases from its initial magnitude in a stretched exponential decay, manifesting the bias-stress effect. The choice of dielectric is found to have little effect on the characteristics of this bias-stress effect, leading us to conclude that the associated charge-trapping process originates within the QD film itself. Measurements of bias-stress-induced time-dependent decays in the drain-source current (I(DS)) are well fit to stretched exponential functions, and the time constants of these decays in n-channel and p-channel operation are found to follow thermally activated (Arrhenius) behavior. Measurements as a function of QD size reveal that the stressing process in n-channel operation is faster for QDs of a smaller diameter while stress in p-channel operation is found to be relatively invariant to QD size. Our results are consistent with a mechanism in which field-induced nanoscale morphological changes within the QD film result in screening of the applied gate field. This phenomenon is entirely recoverable, which allows us to repeatedly observe bias stress and recovery characteristics on the same device. This work elucidates aspects of charge transport in chemically treated lead chalcogenide QD films and is of relevance to ongoing investigations toward employing these films in optoelectronic devices.

Hole Mobility in Accumulation Mode Metal–Oxide–Semiconductor Field-Effect Transistors

The paper deals with the investigation of the mobility in accumulation mode p-channel metal–oxide–semiconductor field-effect transistors (p-MOSFETs). The mobility extracted following the conventional methodology used for the inversion mode p-MOSFETs is actually incorporating a component related to the silicon-on-insulator (SOI) layer. Thus, a very simple and efficient technique to remove the contribution coming from the SOI layer has been proposed. This ultimately led to the extraction of the hole mobility of the accumulation layer. Its study carried out for several doping concentrations revealed a universal behavior similar to the one of the inversion layer. To finish, the contribution of the SOI layer to the measured mobility has been done and revealed a linear trend with the doping concentration. As a result, a simple and very efficient modeling of the mobility in the accumulation mode p-MOSFETs, incorporating the contribution of both the channel and bulk regions, has been achieved.

Carbonaceous field effect transistor with graphene and diamondlike carbon

A carbonaceous field effect transistor, designated as a ‘DLC-GFET’, consisting of a graphene channel and a diamondlike carbon (DLC) top-gate dielectric film was fabricated. A DLC film was formed ‘directly’ onto the graphene channel using our original photoemission-assisted plasma-enhanced chemical vapor deposition (PA-CVD) without forming complex passivation interlayers. The DLC-GFET exhibits clear ambipolar characteristics with a slightly positive shift of the neutral points (Dirac voltages). The Raman analysis suggests that the electrical characteristics are due to unintentional hole doping from the DLC film into the graphene channel. The maximum transconductances per unit device width in the n-channel and the p-channel modes (gmn,max and gmp,max) are 14.6mS/mm and 8.8mS/mm, respectively, with a gate thickness of 48nm and a gate length of 5μm. Formation of the DLC top-gate does not cause obvious damage to the graphene channel. Hence, the PA-CVD method is suitable to form gate dielectrics onto graphene.

Relationship between Thin-Film Transistor Characteristics and Crystallographic Orientation in Excimer-Laser-Processed Pseudo-Single-Crystal-Silicon Films

The characteristics of thin-film transistors (TFTs) fabricated on pseudo-single-crystal (PSX)-Si thin films were examined. The variations of mobility were more than the theoretical values derived from the crystallographic orientation dependence of a bulk Si metal–oxide–semiconductor (MOS) transistor. To clarify the origin of this discrepancy, the relationships between the TFT characteristics and the crystallographic orientation of Si films in the channel region were investigated by using an electron backscattering pattern (EBSP) method. It was found that the surface orientation dependence for the PSX-Si TFT was different from that for a bulk Si MOS transistor, especially for the p-channel mode. A group of TFTs having a nearly {100}-oriented nucleus had a mobility close to those of simultaneously processed silicon-on-insulator (SOI) devices in the p-channel mode as well as in the n-channel mode. In contrast, a group of TFTs having a nearly {110}-oriented nucleus had a low and widely scattered mobility. The reason for these results is that twin boundaries with dislocations are easily generated in a grain grown from a {110}-oriented nucleus in order to compensate for the difference of the growth rates in different directions.

Ambipolar Behavior in Epitaxial Graphene-Based Field-Effect Transistors on Si Substrate

In this research, ambipolar behavior, which is one of graphene's unique characteristics, is studied for the epitaxial graphene formed on 3C-SiC grown on a Si substrate. The graphene channel is believed to be unintentionally p-type-doped at Dirac-point voltages of approximately +0.11 to +0.12 V. However, as drain voltage negatively increases, Dirac point voltage shifts. The drain current in the p-channel mode of operation saturates at a lower level than that in the n-channel mode of operation. These behaviors are caused by asymmetric carrier transport throughout channel-substrate heterojunctions (i.e., graphene, thin n-type SiC layer, and p-type Si substrate) and source/drain Schottky metal contacts. The interface between the p-type Si substrate and n-type SiC has a significant effect on transport in graphene channels. The results may be helpful for understanding transport in the device and for suppressing ambipolar operation, leading to a unipolar FET operation.

Subgap states in transparent amorphous oxide semiconductor, In–Ga–Zn–O, observed by bulk sensitive x-ray photoelectron spectroscopy

We investigated the electronic states in amorphous In–Ga–Zn–O films with high carrier concentrations by optical absorption and hard x-ray photoelectron spectroscopy (HX-PES). Films having different Hall mobilities were prepared and their annealing effects were examined. All HX-PES spectra showed Fermi edge structures and extra subgap densities of states (DOSs). Tail-like structures observed in the optical spectra originate from subgap DOSs (⪢1020cm−3) near valence band maximas (VBMs). Subgap DOSs near VBMs provide a reason why In–Ga–Zn–O thin film transistors show hard saturation in off states and are difficult to operate in an inversion p-channel mode.

Multilayer bipolar field-effect transistors

Field-effect transistors comprising a layer of regioregular poly(3-hexylthiophene) (rr-P3HT) separated from a parallel layer of the soluble fullerene,[6,6]-phenyl C61-butyric acid methyl ester (PCBM) by a layer of titanium suboxide (TiOx), are fabricated by solution processing. Because the TiOx is an electron transporting material and a hole blocking material, this multilayer architecture operates either in the p-channel mode with holes in the rr-P3HT layer or in the n-channel mode with electrons in the PCBM layer.