Catalytic Metal Gate Research Articles

Catalytic Metal‐Gated Nano‐Sheet Field Effect Transistor and Nano‐Sheet Tunnel Field Effect Transistor Based Hydrogen Gas Sensor‐ A Design Perspective

AbstractIn this work, for the first time, the catalytic metal gate (CMG) based nanosheet Field Effect Transistor (NSFET) and nanosheet Tunnel Field Effect Transistor (NSTFET) are proposed for nano‐scale device dimensions, and the different design aspects of catalytic metal gate (CMG)‐based transduction for Hydrogen (H2) sensing are extensively investigated using numerical device simulation. The influence of applied biasing conditions and structural parameter specifications on the sensing performance of CMG‐NSFET and CMG‐NSTFET are methodically analyzed from device electrostatics and carrier transport mechanisms. Furthermore, the relative maximum sensitivity variations with H2‐partial pressure, ambient temperature, and the presence of ambient Oxygen are comprehensively studied. The study reveals that compared to CMG‐NSFET, the CMG‐NSTFET demonstrates a high immunity against bias and doping variations, with a notably higher (> 50%) sensitivity within low H2 partial pressures (10−15 – 10−10 Torr). Next, the sensing performance of CMG‐NSTFET is systematically optimized through a band‐gap and gate‐stack engineering approach, leading to a 180% to 650% sensitivity improvement from lower (10−15 Torr) to higher (10−5 Torr) range of H2 partial pressure. Finally, the performance of optimized CMG‐NSFET and CMG‐NSTFET are extensively benchmarked against other reported nanostructured CMG‐FET and TFET‐based H2 gas sensors, exhibiting a notably higher sensitivity in the proposed sensors.

A highly sensitive MOSFET gas sensor based on charge plasma and catalytic metal gate

AbstractThis manuscript presents, for the first time, a catalytic metal gate‐based charge plasma (CP) MOSFET with improved sensitivity for gas detection applications. In this design, CP refers to the source and drain boundaries being marked by depositing metal electrodes with appropriate work function over the intrinsic silicon film. To sense hydrogen and oxygen gases, palladium (Pd) and silver (Ag) metals are respectively deposited as gate electrodes on P‐CP‐MOSFET and N‐CP‐MOSFET. Further, sensitivity of CP‐MOSFET sensor is determined as if gas molecules are present and the results have been evaluated in comparison with the sensitivity of conventional gas sensor using bulk MOSFET in ATLAS TCAD device simulator. The effect of process variations on sensitivity has also been compared for both devices. The proposed device resolves fabrication complexity issues and offers better sensitivity.

Performance Investigation of Dual Trench Split-Control-Gate MOSFET as Hydrogen Gas Sensor: A Catalytic Metal Gate Approach

In this article, Dual Trench Split-Control-Gate MOSFET (DT-SCG-MOSFET) based hydrogen gas sensor considering catalytic palladium metal gate approach is simulated using SILVACO ATLAS TCAD. The inner gate architecture in addition to the outer control gates provides enhanced carrier control. Shift in surface potential, subthreshold current, linear current and threshold voltage are used to investigate the performance of the proposed gas sensor. The contribution of analog metrices like the transconductance and parasitic capacitances are explored thoroughly. Sensitivity as a function of subthreshold current as well as change in threshold voltage for the presence and absence of hydrogen gas molecules have been discussed. Results exhibit the superiority of the proposed gas sensor compared with the reported models in terms of sensitivity and Ion/Ioff ratio and suitable for hydrogen gas detection.

Design and Investigation of Double Gate Field Effect Transistor Based H2 Gas Sensor Using Ultra-Thin Molybdenum Disulfide

In this article, a low-power hydrogen (H2) gas sensor has been proposed using a two-dimensional (2D) material based Double Gate Field Effect Transistor (2D-FET). It is imperative to highlight that the conventional three-dimensional (3D) materials cannot be scaled down to an ultra-low dimension due to the presence of dangling bonds, surface roughness scattering etc. This creates a major challenge in developing low-dimensional sensors for next generation sensing and computing. In this context, we have developed an extensive simulation model, which articulates the physical phenomena behind a catalytic metal gate-based hydrogen gas sensor using a 2D-FET. A 5 nm thin Molybdenum disulfide (MoS2) film has been used as the channel material for the proposed 2D-FET based gas sensor. The sensor has been modelled by emphasizing on the catalytic metal (Palladium) gate approach, where the work function of the gate metal deposited on top of the channel region varies after the absorption of the hydrogen gas. Moreover, the Technology Computer Aided Design (TCAD) based gas sensor model has been developed by considering a change in the pressure of H2 gas as well. We have also highlighted the effect of Metal/MoS2 contact on sensor performance. In terms of the performance, a maximum threshold voltage (Vth) shift of 100 mV has been obtained against a gas pressure of 10−10 torr, whereas the maximum percentage of change in ION/IOFF is 100. Lastly, the authors have shown the thermal noise characteristics of the gas sensor.

Performance Investigation of Novel Pt/Pd-SiO2 Junctionless FinFET as a High Sensitive Hydrogen Gas Sensor for Industrial Applications

In this paper, a junctionless (JL) Silicon FinFET (Fin Field effect transistor) has been designed as a hydrogen gas (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) sensor. An analytical model has been developed to analyze the response of junctionless FinFET for detection of hydrogen gas. Palladium is used as a catalytic metal gate. The variation in the gas molecule concentration alters the pressure induced on the catalytic metal gate which changes work function of the metal gate. This variation in metal gate work function is used for detecting the presence of the hydrogen gas. Various electrical parameters for which designed gas sensor is analyzed are- surface potential, threshold voltage, drain current, transconductance, output conductance and charge concentration. The sensitivity analysis in terms of threshold voltage and drain current at different pressures is also carried out. The performance of the sensor with catalytic gate metals-palladium (Pd) and platinum (Pt) is analyzed to find which metal gate gives better response as a hydrogen gas sensor. The JL FinFET is also compared with JL Gate All Around (GAA) transistor for threshold voltage and drain current sensitivity.

Investigation of Charge Plasma Enhanced Tunnel Field Effect Transistor for Hydrogen Gas Sensing Application

In this letter, a transducer sensor is introduced that is based on the principle of charge plasma-enhanced tunnel field-effect transistor (CPE-TFET) structure for catalytic metal gate based electrochemical hydrogen (H2) gas detection using numerical device simulation. In the proposed sensor, the induced charge plasma at the source region is exploited for realizing a superior gate control over tunneling junction electrostatics that leads to a drain current sensitivity improvement near an order of magnitude over the conventional (Conv) TFET. The underlying physics of the proposed sensor is explored from a detailed electrostatic analysis of the tunneling junction in the context of gas molecule adsorption. In this effect, the sensitivity is estimated for the different gate and drain biases, and the suitable biasing range of operation is indicated. Furthermore, extensive structural optimization is performed to achieve a design-level understanding of CPE-TFET. Finally, the comparative performance analysis with Conv-TFET and mosfet establishes the inherent superiority of CPE-TFET for H2 gas sensing at different partial gas pressures and temperatures.

Design and analysis of electrostatic-charge plasma based dopingless IGZO vertical nanowire FET for ammonia gas sensing

In this paper, Dopingless Gate All Around (GAA) Vertical Nanowire Field Effect Transistor (VNWFET) is designed with artificial material Indium Gallium Zinc Oxide (IGZO) as a channel material. IGZO channel has high electron mobility compared to more traditional amorphous semiconductors. In VNWFETs, since the channel length (Lch) is characterized vertically, it can be relaxed without area penalty on-chip, which in turn also allows some relaxation in the nanowire diameter while keeping optimum short-channel-effects control. Electrostatic-Charge Plasma technique is used to form a source-drain region on an intrinsic body of IGZO material. At the source side, the N+ region is formed by selecting the appropriate work function of the metal electrode, and at the drain side, the N+ region is formed by giving biasing to the metal electrode. N+ channel dopingless VNWFET with the catalytic metal gate is proposed for ammonia gas sensing. Cobalt, Molybdenum, and Ruthenium are used as a gate electrode in ammonia gas detection due to their high reactivity towards ammonia. Also, we have compared their ON and OFF sensitivity of the proposed device toward the gas adsorption. Due to the presence of gas on the gate, the metal work function of gate metal changes which varies the OFF-current (IOFF), ON-current (ION) and Threshold voltage (Vth) as these are considered as sensitivity parameters for sensing the ammonia gas molecules. The dimensional parameters (radius, and length) and dielectric materials are varied to check the change in device sensitivities. Results show that as the work function varies increases 50, 100, 150, 200 meV and 250 meV for catalytic metal at the gate, the sensitivity is increased.

Highly sensitive dual-FET hydrogen gas sensors with a surface modified gate electrode

Low-power dual-FET type H2 sensors were fabricated, and surface modification techniques were developed to control the morphology of the catalytic metal gate. The differential outputs between the sensing FET and the reference FET were preserved even under a thermal change (from 50 °C to 150 °C) due to the same dependence of the electrical characteristics. The proposed sensor design showed low power consumption (45.5 mW 150 °C) by complete heat isolation. The sensors gave stable responses to H2 gas over a wide temperature range, and the temperature of optimal response in micro-heater operation was approximately 150 °C. The surface of the catalytic metal gate was modified with solution based methods using a poly-styrene (PS) nano-beads suspension. The maximum drain current changes of the FET sensors with a nano-bumpy Pd film and a flat-surface Pd film were 164.6 μA and 128.2 μA to 5000 ppm hydrogen, respectively. The gas sensing characteristics of the FET sensor with the nano-bumpy Pd film were much higher than those of the FET sensor with the thin film due to the nano-porosity of the catalytic metal film.

Gate-All-Around Nanowire MOSFET With Catalytic Metal Gate For Gas Sensing Applications

In this paper, gate-all-around (GAA) MOSFET with catalytic metal gate is proposed for enhanced sensitivity of gas sensor. P-channel GAA MOSFET with palladium (Pd) metal gate is used for hydrogen sensing and n-channel GAA MOSFET with silver (Ag) metal gate is used for Oxygen sensing. The GAA nanowire MOSFET has already been demonstrated experimentally for biosensing and chemical sensing applications. However, cylindrical GAA MOSFET with catalytic metal gate for gas sensing applications is proposed for the first time in this paper. An analytical model is developed for both p-channel and n-channel GAA MOSFET to calculate the sensitivity of the device in the presence of gas molecules and analytical model is verified with the simulation results of ATLAS-3D. Sensitivity of the GAA MOSFET gas sensor is compared with the conventional bulk MOSFET gas sensor and impact of the radius of the silicon pillar on the sensitivity of the GAA MOSFET is also studied.

Design and Fabrication of MOSFET Type Hydrogen Gas Sensor Using MEMS Process

In this study, MOSFET type micro hydrogen gas sensors with platinum catalytic metal gates were designed, fabricated, and their electrical characteristics were analyzed. The devised MOSFET Hydrogen Sensors, called MHS-1 and -2, were designed with a platinum gate for hydrogen gas adsorption, and an additional sensing part for higher gas sensitivity and with a micro heater for operation temperature control. In the electrical characterization of the fabricated Pt-gate MOSFET (MHS-1), the saturated drain current was 3.07 mA at 3.0 V of gate voltage, which value in calculation was most similar to measurement data. The amount of threshold voltage shift and saturated drain current increase to variation of hydrogen gas concentration were calculated and the hydrogen gas sensing properties were anticipated and analyzed. (Received October 14, 2010)

Catalytic Forming Gas Anneal on III-V/Ge MOS Systems

AbstractCatalytic-FGA, a combination of the standard forming gas anneal with a catalytic metal gate, has been applied to study the hydrogen passivation of III-V/Ge MOS systems. Pd (or Pt) metal gate catalytically dissociates molecular hydrogen into atomic hydrogen atoms, which then diffuse through the dielectric layer and neutralize certain semiconductor/dielectric interfacial defects. MOS systems with various interfacial qualities, including lattice-matched (n/p) In0.53Ga0.47As/10nm ALD-Al2O3 (or ZrO2)/Pd capacitors, an undoped Ge/˜1nm GeO2/4nm ALD-Al2O3/Pt capacitor, and an nGe/8nm ALD-Al2O3/Pt capacitor are fabricated to evaluate the effectiveness of C-FGA.

MISFET Type H2 Sensor Using Pd-black Catalytic Metal Gate for High Performance

not Available.

The influence of catalytic activity on the phase transition governed binary switch point of MISiC-FET lambda sensors

A metal insulator silicon carbide field effect transistor (MISiC-FET) sensor with a catalytic metal gate is currently under development for detecting the lambda value, or air-to-fuel ratio, of gasoline exhausts. It has been noticed that a change from a low to a high signal level of the sensor occurs at a lambda value above 1.00, which is an oxidizing atmosphere. The exact location of the switch point depends both on the kind of gas and gas concentrations chosen to obtain a specific lambda value. The switch point would rather have been expected at 1.00, which is at stoichiometry, irrespective of the composition of the gas mixture. The origin of this phenomenon is studied here by exposing the sensor to lambda stairs while changing different operating parameters. An increase in catalytic activity has been observed to move the switch point of the device towards a lambda value of 1.00. A similar effect is achieved when decreasing the flow or increasing the temperature of operation of the device. The behavior is explained through the introduction of mass transport limitations in the measurement cell, and the difference in diffusion constants and sticking coefficients among the gases when reaction limitation prevails.

Pt/SnO&lt;sub&gt;2&lt;/sub&gt;/SiC/Niヘテロ構造を用いた高温高感度NOxガスセンサ

In order to develop a high temperature (200°C˜400°C) and high sensitive NOx gas sensor with SiC based junction structure, a hetero-junction structure, Pt/SnO2/SiC/Ni, was investigated and compared with the catalytic metal gate Schottky structure (Pt/SiC/Ni) sensor. It was found that the hetero-junction device showed much higher sensitivity to NO2 gas compared with the Schottky junction structure sensor, whereas Schottky structure device had better sensitivity to NO gas than a hetero-junction structure sensor. These results suggest that selective detection of NO and NO2 gases may be attained with these different structure devices.

Hydrogen in the Wide Bandgap Semiconductor Silicon Carbide

In this paper we give a review of our recent results related to the incorporation of hydrogen (H) in silicon carbide (SiC) and its interaction with acceptor doping atoms and implantation induced defects. Hydrogen is an abundant impurity in the growth of epitaxial SiC since it is present in the precursor gases and since H2 is used as the carrier gas. High concentrations of hydrogen are indeed incorporated into highly doped p-type epi-layers and it is shown that the main source is the carrier gas. Furthermore, it is revealed that the entire substrate becomes homogeneously filled with hydrogen during growth and that this hydrogen is more thermally stable than that in the epi-layer. Incorporation of hydrogen from an H2 ambient, at temperatures considerably lower than those used for epitaxy, is also demonstrated in p-type samples coated with a catalytic metal film. This effect is most likely the cause for the increased series resistance observed in p-type SiC Schottky sensor devices using a catalytic metal gate after annealing at 600 °C in a H2 containing ambient. Hydrogen is found to passivate the acceptors Al and B by forming electrically neutral H-acceptor complexes. Unlike in Si and GaAs, the two H-acceptor complexes in SiC exhibit very different dissociation energies, suggesting that the atomic configurations of the complexes are significantly different. The migration of mobile hydrogen in the presence of externally applied, or internal built-in, electric fields further reveals that hydrogen is present as H+ in p-type SiC. Finally, the redistribution and subsequent out-diffusion of low energy implanted 1H and 2H is investigated. Two annealing phases for the redistribution are observed, and the activation energies for the processes are extracted.

High-Temperature SiC MOSFET Gas Sensors

ABSTRACTDue to tightening restrictions on combustion exhaust emissions, low-cost sensors are desired for monitoring NOx production in high-temperature exhaust streams. This paper reports the characterization of Silicon Carbide MOSFET NO sensors for use in combustion exhaust monitoring. SiC depletion-mode MOSFETs were fabricated using a thermally-grown silicon dioxide gate dielectric and a Pt catalytic metal gate electrode. SiC MOSFET gas sensors were characterized at temperatures as high as 525°C in an ambient of synthetic air and NO (50–200 ppm) for 30 hours with no degradation.

The Effect of Hydrogen Diffusion in p- and n-Type SiC Schottky Diodes at High Temperatures

We present here the effect of a hydrogen anneal at 600degreesC for Schottky sensor devices based on n- and p-type 4H SiC. The devices have gate contacts of Ta/Pt, or TaSix/Pt. The catalytic metal gate dissociates hydrogen and thus promotes diffusion of hydrogen atoms into the SiC, where the atoms will trap or react with different impurities, defects or surface states. This will change parameters such as the carrier concentrations, the defect density of the material or the surface resistivity at the SiC/SiO2 interface. The current-voltage and the capacitance-voltage characteristics were measured before and after annealing in hydrogen and oxygen containing atmosphere, and the results show a reversible effect in the I-V characteristics.

Chemical images

Chemical sensors can be used to generate a vast amount of information about the emissions from bio- and chemical processes, from food and bacteria and from a number of products. These emissions are either wanted or should be avoided. Wolfgang Göpel was one of those who recognized early the large potential of chemical sensor arrays and different modes of operation of a given sensor. We describe how large area field effect devices, with catalytic metal gates, can be used for the construction of a response image of a gaseous emission. More specifically, we discuss the new possibilities obtained through the use of catalytic metals with a gradient in thickness. Some basic features of such sensing surfaces are demonstrated and, finally, time-dependent response images from aging meat are used to demonstrate the potential of the method used. It is based on a scanning light pulse technique (SLPT) which measures local polarization or work function changes in two dimensions and, e.g. a sensing surface consisting of bands of different catalytic metals with a gradient in thickness.

The influence of mass transport processes on the response to gas mixtures of field-effect devices with large-area catalytic metal gates

A model of how response maps of gas mixtures obtained from large-area field-effect devices with thin catalytic metal gates are affected by the mass transport processes in the gas above the gate has been derived. The model is based on a numerical calculation of the local analyte concentration in the vicinity of the gate of the device. It is found that the catalytic activity of the gate metal may give rise to substantial lateral variations in the analyte concentration at the gate. The varying analyte concentration offers an explanation to the shape of the response maps obtained in earlier experiments. The model is utilized to predict how the analyte mass fraction at the gate, and thus the response maps, should be affected by the gas velocity, the catalytic surface area, and the local consumption rate of analyte at the gate. It is also shown that the geometry of the measurement cell that surrounds the sensing device during measurements may affect the response pictures. The use of the model in connection with distributed chemical sensing and determination of reaction rates is briefly discussed.

NO&lt;sub&gt;x&lt;/sub&gt; Detection with Schottky Diodes and Heterojunction Structures

We investigated thin catalytic metal gate Schottky diodes and pn heterojunctions for NOx detection. Thin Pt-Pd/Si/Al Schottky diodes were employed successfully to detect NO2 concentrations from 6ppm to 30ppm and NO concentrations from 50 to 250ppm, with a response roughly proportional to the logarithm of gas concentration. We investigated the fabrication of the diodes on a porous Si surface and the formation of a Si/WO3 heterojunction as possible ways to improve sensitivity. Diodes fabricated on porous Si showed slightly higher sensitivity to NO2. The sensitivity of a Pt-Pd/WO3/Si/Al heterojunction was comparable to the sensitivity of the Schottky diodes. The differences between the sensing mechanisms of these structures were also investigated and the results suggest that they provide different possibilities to enhance the sensitivity. An advantage of these sensors is to operate at room temperature. Moreover, the semiconductor junction structure is convenient to make smaller and intelligent sensors. Therefore, these structures may be considered for future development of NOx gas sensors at room temperature with miniaturization, integration and power saving features.