Showing papers in "Solid-state Electronics in 2020"

SO2 gas sensing characteristics of FET- and resistor-type gas sensors having WO3 as sensing material

Abstract: Sensing characteristics of the SO2 gas are investigated using a horizontal floating-gate FET-type gas sensor. SO2 gas sensing characteristics of the resistor-type gas sensor, a conventional sensor, fabricated on the same wafer are also investigated and compared with the FET-type gas sensor. The 18-nm-thick WO3 deposited using a radio frequency magnetron sputtering method is used as the sensing material. The SO2 gas sensing characteristics are examined while varying the operating temperature, the concentration of the SO2 gas, and the pre-bias (Vpre). The sensing mechanism for detecting the SO2 gas in an FET-type gas sensor is examined. Both sensors are able to detect up to 10 ppm of SO2 gas, and the FET-type sensor shows significantly improved gas response by using the pre-bias scheme.

On the modelling of temperature dependence of subthreshold swing in MOSFETs down to cryogenic temperature

Abstract: A comprehensive analysis of the MOSFET subthreshold swing for a 2D subband with exponential band tail of states is first proposed. Then, a compact analytical expression for the subthreshold swing as a function of temperature is derived, well accounting for both its cryogenic temperature saturation and classical higher temperature increase. Moreover, a generalized subthreshold swing calculation applicable to the situation where the MOSFET drain current should be evaluated from the conductivity function within the Kubo-Greenwood formalism is developed.

Scaled resistively-coupled VO2 oscillators for neuromorphic computing

Abstract: New computation schemes inspired by biological processes are arising as an alternative to standard von-Neumann architectures, to provide hardware accelerators for information processing based on a neural networks approach. Systems of frequency-locked, coupled oscillators are investigated using the phase difference of the signal as the state variable rather than the voltage or current amplitude. As previously shown, these oscillating neural networks can efficiently solve complex and unstructured tasks such as image recognition. We have built nanometer scale relaxation oscillators based on the insulator–metal transition of VO2. Coupling these oscillators with an array of tunable resistors offers the perspective of realizing compact oscillator networks. In this work we show experimental coupling of two oscillators. The phase of the two oscillators could be reversibly altered between in-phase and out-of-phase oscillation upon changing the value of the coupling resistor, i.e. by tuning the coupling strength. The impact of the variability of the devices on the coupling performances are investigated across two generations of devices.

Nanowire & nanosheet FETs for ultra-scaled, high-density logic and memory applications

Abstract: We report on vertically stacked lateral nanowires (NW)/nanosheets (NS) gate-all-around (GAA) FET devices as promising candidates to obtain a better power-performance metric for logic applications for advanced sub-5 nm technology nodes, in comparison to finFETs. In addition, vertical NW/NS GAA FETs appear particularly attractive for enabling highly dense memory cells such as SRAMs (with improved read and write stability), and as the selector devices for ultra-scaled MRAMs with lower energy consumption values. These cells can be manufactured by a cost-effective, co-integration scheme with a triple-gate finFET or a lateral NW/NS GAA FET high-performance logic platform for increased on-chip memory content.

Effects of recess depths on performance of AlGaN/GaN power MIS-HEMTs on the Si substrates and threshold voltage model of different recess depths for the using HfO2 gate insulator

Abstract: Three types of E-mode AlGaN/GaN MIS-HEMTs with different barrier depths and conventional HEMT were fabricated on the Si substrates. HfO2 gate insulator with a thickness of 30 nm was grown by plasma enhanced atomic layer deposited (PEALD). Characteristics of the four devices with different recess depths are analyzed. The MIS-HEMT with barrier layer thickness of 3 nm features good comprehensive performance. The threshold voltage (Vth) is 1.8 V, the drain current density is 480 mA/mm and the figure of merit (FOM) is 363 MW/cm2. When the barrier thickness is 0 nm, the Vth is up to 3.7 V. A calculation model of threshold voltage for recessed MIS-HEMTs is proposed. When the barrier layer thickness is 6 nm, the calculated value of Vth was 0.3 V which is in good match with the experimental value of 0.4 V. The proposed model provides guidelines for the AlGaN/GaN MIS-HEMTs designs.

Simulation of the effect of parasitic channel height on characteristics of stacked gate-all-around nanosheet FET

Abstract: By using technology computer aided design (TCAD) simulation, the aim of this paper is to investigate the effect of Si parasitic channel, which is placed under stacked nanosheet channels, on electrical characteristic of stacked nanosheet GAA FETs. We have controlled the parasitic channel height, and evaluated the effect on electrical performance of the device. Trade-off in performance of the nanosheet FET is observed: the increase in parasitic channel height results in improvement in subthreshold swing and on/off ratio, while the increase in capacitance brings worse RC delay and active power. The parasitic channel height control in devices with ground plane doping is also investigated.

Poly(vinyl alcohol)-gated junctionless Al-Zn-O phototransistor for photonic and electric hybrid neuromorphic computation

Abstract: The hardware implementation of biological synapses is very necessary for a new brain-like neuromorphic computation system. In recent years, optoelectronic synaptic devices have become the application platform for next generation neuromorphic system and artificial neural network. Here, a new kind of photoelectronic synaptic transistors are proposed using the Al-Zn-O (AZO) as coplanar gate and the laterally-coupled poly (vinyl alcohol) (PVA) electrolyte membrane as neurotransmitter. The key synaptic functions such as excitatory postsynaptic current (EPSC) and paired-pulse-facilitation (PPF) were successfully emulated. More importantly, by exposing an ultraviolet (UV) laser, the transformation of short-term memory (STM) to long-term memory (LTM) can be mimicked in our neuromorphic devices. Furthermore, an energy-band diagram is finally proposed for a better understanding of the underlying mechanism of LTM behavior. These results represent an important step toward the next-generation neural networks enabled by photo-electric hybrid nano-electronics, and point to the potential of more sophisticated neuromorphic computations.

Enhanced charge-transportation properties of low-temperature processed Al-doped ZnO and its impact on PV cell parameters of organic-inorganic perovskite solar cells

Abstract: The present work highlights the potential of low-temperature processed Al-doped ZnO (AZO) nanoparticles (NPs) for application in organic-inorganic perovskite solar cells (PSCs). ZnO nanostructured electron-transporting layer (ETL)-based PSCs are superior to ZnO film-based PSCs owing to their relatively lower cost, simpler deposition process, milder sintering temperatures, and higher electron mobility. Moreover, the PSCs based on ZnO nanostructure ETLs are more stable than ZnO film-based PSCs because perovskite films can be easily decomposed into PbI2 during the annealing process. Al doping in ZnO can reduce the recombination at the ETL/perovskite interface. Thus, low-temperature processed AZO NPs were used as the ETLs for PSCs, and the effects of Al doping on the performance and photovoltaic parameters of PSCs were investigated. The lowest transmission loss was observed for the AZO sample with an Al/Zn molar ratio of 2%, while a higher transportation rate was obtained for the Al/Zn molar ratio of 5%. The effectiveness of Al doping was demonstrated by a conversion efficiency (η) of 13.91% for the Al/Zn molar ratio of 2% (η = 12.28% for ZnO). Moreover, the short-circuit current density (from 18.40 to 19.36 mA/cm2) and fill factor (from 67.87 to 71.18%) increased. The value of shunt resistance gradually increased (from ~799 to 1248 Ωcm2) by Al doping. The values of diode ideality factor (from 2.3221 to 2.3175) and reverse saturation current density (from 11.97 × 10−10 to 7.95 × 10−10 A/cm2) decreased by Al doping, indicating a reduction in the recombination loss. The lowest series resistance was obtained for Al/Zn molar ratio of 2%.

All MOCVD grown Al0.7Ga0.3N/Al0.5Ga0.5N HFET: An approach to make ohmic contacts to Al-rich AlGaN channel transistors

Abstract: We report a gate recessed Al0.7Ga0.3N/Al0.5Ga0.5N heterostructure field effect transistor (HFET) with a graded contact cap layer grown by metal organic chemical vapor deposition (MOCVD) on AlN/Sapphire substrate. A low specific contact resistivity ρc of 2.1 × 10−5 Ω·cm2 is demonstrated with current injection from the top of the Al0.7Ga0.3N barrier to the Al0.5Ga0.5N channel. The device with a gate length of 160 nm exhibits a drain current density at gate shorted to source (ID,SS) of 420 mA/mm, a cutoff frequency fT of 20 GHz, and a maximum oscillation frequency (fmax) of 40 GHz. The same device has a three terminal off-state gate-to-drain breakdown voltage of 170 V, corresponding to an average breakdown field (FBR) of 2.8 MV/cm between the gate and drain, due to drain induced barrier lowering effect. Devices with a gate length of 1 µm demonstrate a gate to drain breakdown voltage of 195 V or an average breakdown field of 3.9 MV/cm. This work provides a way to make ohmic contacts to Al-rich AlGaN channel heterojunction transistors for high power and high frequency applications.

Phenol red based hybrid photodiode for optical detector applications

Abstract: In this study, the phenol red (PR) dye film has been deposited on n-type silicon wafer and SEM, XRD measurements of the film have taken. Then, the PR/n-Si photodiode has been fabricated and (dark) electrical and photoresponse characterization has been analysed. The current-Voltage (I-V) measurements have been carried out at varied light power ranging from 100 mW/cm2 to 400 mW/cm2. Rectification ratios (RR) have been determined as a function of illumination intensities and they are determined as 115.47 for 100 mW/cm2 and 30.26 for 400 100 mW/cm2, respectively. The ideality factor and the barrier height of the Co/PR/n-Si photodiode have been determined as 2.80 and 0.52 eV, respectively in dark. Therefore, it has been seen that the PR/n-Si photodiode performances are strongly dependent on the incident optical power. Namely, the current density has increased remarkably with the power of light at the same reverse bias voltage and this behavior is explained by strong capability of converting a light signal into an electrical for the PR/n-Si photodiode device. Responsivity (R) and detectivity (D*) of the PR/n-Si photodiode are also plotted as a function of illumination intensities for reverse biases and it is found that both parameters are dependent on the illumination intensity. Finally, the capacitance–voltage (C-V) characteristics of the device have been carried out at various frequencies. Obtained experimental results indicate that the PR dye can be used in various optoelectronic applications.

Contact resistance extraction of graphene FET technologies based on individual device characterization

Abstract: Straightforward contact resistance extraction methods based on electrical device characteristics are described and applied here to graphene field-effect transistors from different technologies. The methods are an educated adaptation of extraction procedures originally developed for conventional transistors by exploiting the drift–diffusion-like transport in graphene devices under certain bias conditions. In contrast to other available approaches for contact resistance extraction of graphene transistors, the practical methods used here do not require either the fabrication of dedicated test structures or internal device phenomena characterization. The methodologies are evaluated with simulation-based data and applied to fabricated devices. The extracted values are close to the ones obtained with other more intricate methodologies. Bias-dependent contact and channel resistances studies, bias-dependent high-frequency performance studies and contact engineering studies are enhanced and evaluated by the extracted contact resistance values.

Improved organic solar cell by incorporating silver nanoparticles embedded polyaniline as buffer layer

Abstract: The role of silver nanoparticles (AgNP) in polyaniline (PANI) as a buffer layer for ITO/AgNP-PANI/PANI/Al solar cell was investigated. It is observed that AgNP-PANI buffer layer significantly improves the electrical parameters such as diode-ideality factor, series-resistance, energy-barrier height, and shunt-resistance as a growing function of AgNP concentration. On-the-other hand oppose to the dark current-voltage response, 0.5% concentration of AgNP in buffer layer shows the most optimum photovoltaic response and cause to increase the power conversion efficiency (PCE) nearly 5 times compared to same solar cell without buffer layer. Such improvements in electrical parameters can be interpreted as the reduction in interfacial trap states as well as enhancement in interfacial dipole-moment by AgNP embedded buffer layer for given photovoltaic device. While, the observed optimum photovoltaic behavior at 0.5% AgNP concentration is may be due to the trade-offs between gains and losses for optical absorption enhancement, self-absorption heating and interface recombination losses respectively. It is also observed that the AgNP embedded PANI buffer layer approach is an effective solution to lower the photovoltaic degradation and hence improves the stability of the photovoltaic devices.

Effect of adding ZHS microcubes on ZnO nanorods for CO2 gas sensing applications

Abstract: Conventionally, the catalytic promotion of semiconductor metal oxide-based CO2 sensors response is simply based on chemical reaction. In most realistic applications, the sensors are operated in both sensing gas and light surrounding. Hence, we try to use a new type of catalyst, such as ZnSn(OH)6 (ZHS) has both chemical and photo catalytic functions to improve gas response more significantly. In this work, ZnO nanorods are deposited on p-type silicon substrate with and without ZHS microcubes covered on the top. The effects of adding the ZHS microcubes on CO2 sensing response have been studied in detail with experimental measurements. Experimental results show that the added ZHS microcubes promote CO2 response up to 350%, which is higher than the reported CO2 sensors with or without metal catalyst.

Robust magnetic field-free switching of a perpendicularly magnetized free layer for SOT-MRAM

Abstract: We investigate the robustness of a purely electrical field-free switching of a perpendicularly magnetized free layer based on SOT. The effective magnetic field which leads to deterministic switching of a rectangular as well as of a square free layer is created dynamically by a two-current pulse scheme. It is demonstrated that the switching is very robust, being insensitive to fluctuations of the write pulses’ durations and to relatively large variations of the heavy metal wires’ dimensions. Furthermore, it remains reliable for a wide range of synchronization failures between the pulses. The combination of a rectangular free layer shape with a partial overlap with the second current line accelerates the switching of the cell allowing a fast, 0.25 ns, switching.

Tailoring PEDOT:PSS polymer electrode for solution-processed inverted organic solar cells

Abstract: Conductivity and work function of the conductive polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), has been investigated for a top electrode of the solution-processed organic solar cells (OPV). It has been found that both conductivity and work function could be changed by adjusting the mixing ratio of different commercial grade PEDOT:PSS such as PH 1000 and AI 4083. A 2:1 vol ratio of PH 1000 and AI 4083 mixture provided the conductivity of 443 S/cm (corresponding sheet resistance (Rsh) of 260 Ω/sq) and the work function of 5.09 eV. Therefore, this PEDOT:PSS mixture may work as both a hole transport layer (HTL) and anode electrode of the OPV. For verifying, all-solution-processed bulk heterojunction (BHJ) inverted OPVs were fabricated using developed PEDOT:PSS conductive polymers as both HTL and anode top electrode. Under the AM1.5G spectrum calibrated 100 mW/cm2 illumination, fabricated all-solution-processed OPV provides a best photo-conversion efficiency (PCE) of 2.04% accounted from an open circuit voltage (Voc) of 576 mV, a short circuit current (Jsc) of 6.91 mA/cm2, and a fill factor (FF) of 51.2%. In addition, the final OPV exhibits semitransparency due to no metal electrode on top and transparency of the conductive polymer.

Resistive switching behavior of solution-processed AlOx and GO based RRAM at low temperature

Abstract: This paper reports on resistive switching behavior observed in resistive random access memory (RRAM) devices fabricated with aluminum oxide (AlOx) and graphene oxide (GO) dielectric films, which were solution-processed under low annealing temperatures of 250 °C and 50 °C for AlOx and GO dielectric films, respectively. As representative of metal oxide and two-dimensional material, a detailed study and comprehensive comparison in view of resistive switching performance has been conducted for AlOx and GO based RRAM, including operation voltage, resistance distribution, resistance ratio, conduction mechanism and retention/endurance property. A smaller operation voltage and better stability were demonstrated in AlOx based RRAM devices while higher resistance magnitude of high resistance state (HRS) and resistance ratio were observed in GO based RRAM devices. The current study opens up promising applications of environmental-friendly solution-processed AlOx and GO films with lower energy consumption for non-volatile memory (NVM).

Surface Ge-rich p-type SiGe channel tunnel field-effect transistor fabricated by local condensation technique

Abstract: In this study, tunnel field-effect transistor (TFET) which has surface Ge-rich SiGe nanowire as a channel has been demonstrated. There are improvements in terms of on-current and subthreshold swing (SS) comparing with control groups (constant Ge concentration SiGe TFET and Si TFET) fabricated by the same process flow except for the channel formation step. In order to obtain the concentration-graded SiGe channel, Ge condensation method which is a kind of oxidation is adopted. The rectangular shape of the channel becomes a rounded nanowire through the Ge condensation process. The TFET with the concentration-graded SiGe channel can improve drive current due to a smaller band gap at the Ge-condensed surface of the channel compared to Si or non-condensed SiGe channel TFET.

Performance of pyrocatechol violet and carminic acid sensitized ZnO/CdS nanostructured photoactive materials for dye sensitized solar cell

Abstract: In this study, ZnO and CdS deposited ZnO nanostructured material was successfully synthesized by using co-precipitation and ultra-sonication methods, respectively. A comparative study of the sensitization of ZnO and nanostructured ZnO/CdS with two different dyes (carminic acid and pyrocatechol violet) and applications of the synthesized material in solid state dye sensitized solar cells (DSSCs) are reported here. The characterization of the materials was performed by using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The SEM and TEM results showed that surface of ZnO nano spheres is well covered with CdS. UV–visible spectrum showed the rise of a new optical band due to CdS deposition which effectively tuned the band gap of ZnO from 3.12 eV to 1.877 eV. XRD analysis revealed the successful formation of hexagonal phases of CdS and ZnO. The materials were applied as photoanodes in DSSCs with and without dye sensitization. P3HT (Poly (3-hexylthiophene) was used as a hole conducting polymer. CdS deposition and sensitization with different dyes showed a significant effect on the overall efficiency of fabricated devices. The ZnO/CdS based DSSC sensitized with carminic acid showed a current density (Jsc) of 8.72 mA/cm2 with an open circuit voltage (Voc) of 0.43 V and an overall efficiency of 1.42%. While the same photoanode material sensitized with pyrocatechol violet gave Jsc value of 9.13 mA/cm2 with a Voc of 0.39 V and an overall efficiency of 1.55%.

Modeling source/drain lateral Gaussian doping profile of DG-MOSFET using Green’s function approach

Abstract: Present work has used Green’s function approach to derive a two-dimensional analytical model of the double gate (DG) MOSFET at the subthreshold regime of operation that considers the effect of inevitable source/drain (S/D) lateral Gaussian doping profile. The non-integrable Gaussian term has been converted into an integrable function for accurate Fourier coefficient calculation which is then used to determine the potential equations of all three regions. These equations are then utilized to formulate channel current (Isub), the threshold voltage (Vt) roll off and subthreshold slope (SS) of the device. The effects of lateral Gaussian profile at different gate length (L), and for devices with different combinations of oxide thickness (tox) and channel thickness (tsi) have been investigated. The results show that the S/D Gaussian doping profile has severe effects at scaled gate lengths, where gate electrostatic control is of paramount importance.

Comprehensive predictive modeling of resistive switching devices using a bias-dependent window function approach

Abstract: Development of accurate models for resistive switching devices (memristors) is a research topic of utmost interest. Behavioral models usually employ window functions (WFs) to capture the dependency of the resistance switching-rate on the bias conditions. Several WFs have been published so far, all of them being functions of just the state variable(s), ignoring the effect of the applied signal magnitude in dynamic behavior. In this context, we describe in an extended manner a generalized concept of bias-dependent WFs, designed to enhance behavioral models in capturing rich dynamic time-response of memristors. We present a specific WF formulation and evaluate its effect on the performance of threshold-type models of voltage-controlled bipolar memristor, in simulations with LTSPICE. The obtained results not only reflect the accumulated effect of the applied signal and the proper saturation of the device at voltage-dependent levels, but are also quantitatively in line with experimental data taken from commercial self-directed channel (SDC) memristors of Knowm Inc.

Implementation of homeostasis functionality in neuron circuit using double-gate device for spiking neural network

Abstract: The homeostatic neuron circuit using a double-gate MOSFET is proposed to imitate a homeostasis functionality of a biological neuron in spiking neural networks (SNN) based on a spike-timing dependent plasticity (STDP). The threshold voltage (Vth) of the double-gate MOSFET is controlled by independent two-gate biases (VG1 and VG2). By using Vth change of the double-gate MOSFET in the neuron circuits, the fire rate of the output neuron is controlled. The homeostasis functionality is implemented by the operation of multi-neuron system based on the proposed neuron circuit. Through the SNN based on STDP using MNIST datasets, it is demonstrated that the recognition rate (~91%) of the SNN with the proposed homeostasis functionality is higher than that (~79%) of the SNN without the proposed homeostasis functionality. Also, the results of the recognition rate with the variations (σ/μ

Trade-off between interfacial charge and negative capacitance effects in the Hf-Zr-Al-O/Hf0.5Zr0.5O2 bilayer system

Abstract: Recently, negative capacitance (NC) effect in the dielectric/ferroelectric (DE/FE) bilayer system has received significant attention due to its potential in achieving sub- 60 mV/decade subthreshold swing in FETs as well as extremely large capacitance density in dynamic random-access memory (DRAM). However, such reports, to date, are primarily based on conventional perovskite FE materials which are not compatible with the present CMOS technology. Herein, we study the interfacial charge density ( σ i ) and negative capacitance (NC) effect in CMOS compatible Hf-Zr-Al-O (DE) /Hf0.5Zr0.5O2 (FE) bilayer system. The DE layer of various thicknesses (5–20 A) was deposited on the top of FE layer (100 A) and the DE layer thickness was found to play a crucial role in determining σ i . The NC effect in the aforesaid DE/FE system was suppressed due to the contribution of σ i . The σ i at the interface of the DE layer and FE layer was found to be in the range of −0.57 Cm−2 to −0.18 Cm−2 for the DE thickness range of 5–20 A.

Post-process porous silicon for 5G applications

Abstract: The interest of 5G in centimeter and millimeter waves relies on large blocks of available spectra and thus increased bandwidth. At these frequencies, the dielectric and conductive losses of the substrate can greatly degrade the performances of RF circuits. With high electrical resistivity and low relative permittivity, porous silicon is an ideal candidate as a high-quality RF substrate. This paper presents an innovative technique of post device fabrication integration of porous silicon (POST-PSi) with the substrate. The frontside is not involved in porous layer growth and therefore the integrity of the RF circuitry is not impacted by the POST-PSi process. A comparison of the RF performances with benchmark trap-rich (TR) RF silicon substrate is presented. In addition to its compatibility with standard microfabrication processes and stable final structure, POST-PSi provides characteristics of low losses, high isolation and very high linearity, unmatched by any other silicon-based substrate. Finally, the substrate’s RF performance is evaluated at high temperature, and POST-PSi substrate linearity is shown to remain sufficiently high for RF and 5G applications up to 175 °C.

The thermoelectric-photoelectric integrated power generator and its design verification

Abstract: This paper introduces the integrated generator and its design verification. In order to analyze the output performance of the thermoelectric generator, the design verification is carried out using ANSYS finite element simulation. In the simulation of traditional thermocouple structure, the maximum power factor is 8.99 × 10−3 μWcm−2K−2. In the simulation of I-shaped thermocouple structure, the maximum power factor is 11.39 × 10−3 μWcm−2K−2. It verifies that compare with the traditional thermocouple, the I-shaped thermocouple can increase the maximum power factor. The thermoelectric-photoelectric integrated generator is fabricated by one multi-step MEMS process. The bottom of integrated generator is the light energy collector. The top of integrated generator is the thermal energy collector. Polyimide is coated on the upper end of the thermopile to make the heat transfer smoothly. It also make the temperature difference between the front side and back side larger. In the experiment, the thermoelectric and photoelectric properties of the generator are tested at room temperature. The maximum power factor of the generator is 7.81 × 10−3 μWcm−2K−2. The photoelectric efficiency is 7.58%. The I-shaped thermocouple structure reduces contact resistance and increases the maximum power factor of the thermoelectricity. In practical use, this generator can power portable sensors.

Leakage current mechanisms of groove-type tungsten-anode GaN SBDs with ultra low turn-ON voltage and low reverse current

Abstract: In this work, we report a high-performance lateral GaN Schottky barrier diode (SBD) with a low turn-on voltage (VON) of 0.39 V and low reverse current. Meanwhile we have proposed a model to comprehend the leakage current mechanism in this GaN SBDs. The reverse current transport mechanism was analyzed by temperature-dependent current–voltage (T-I-V) measurements. The results indicate that reverse current is dominated by thermionic emission (TE), Frenkel–Poole (FP) emission and trap assisted tunneling (TAT) near zero bias, at low and high reverse bias, respectively. The thermionic field emission (TFE) is found to be the main mechanism near the breakdown voltage (BV). The comparison shows Al2O3 passivation layer can effectively reduce leakage current.

Efficient compact modelling of UTC-photodiode towards terahertz communication system design

Abstract: Monolithic optoelectronic integrated circuits, OEICs are seen as key enabling technologies to minimal power loss criteria. Monolithic OEICs combine, on the same die, cutting-edge optical devices and high speed III-V electronics able to generate terahertz signal targeting beyond-5G networks. Computationally efficient compact models compatible with existing software tool and design flow are essential for timely and cost-effective OEIC achievement. The analog nature of photonic devices wholly justifies the use of methodologies alike the ones employed in electronic design automation, through implementation of accurate (and SPICE-compatible) compact models. This multidisciplinary work, describes an efficient compact model for Uni-Traveling Carrier photodiodes (UTC PD) which is a key component for OEICs. Its equations feature the UTC PD electronic transport and frequency response along with its photocurrent under applied optical power. It also dynamically takes into account the device junction temperature, accounting for the self-heating effect. Excellent agreement between model and measurements as well as model scalability (several geometries have been validated) has been achieved that marks the first demonstration of a multi-physics, computationally efficient and versatile compact model for UTC-PDs.

Comparative study on performance of AlGaN/GaN MS-HEMTs with SiNx, SiOx, and SiNO surface passivation

Abstract: A comparative investigation on device characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with SiNx, SiOx, and SiON passivation by using plasma enhanced chemical vapor deposition (PECVD) technique is conducted. The electrical performance of passivated GaN HEMTs are evaluated through DC current-voltage, pulsed current-voltage, and small-signal measurements. Obvious increases of 10.5% in drain current and of 8.6% in transconductance are observed for SiON passivated HEMT as compared with both the SiOx and SiNx passivated HEMTs. The SiOx passivated device is found to have lowest gate leakage current as well as off-state drain leakage current as compared to SiNx and SiON passivated devices. However, the pulsed I-V measurement shows a severe current collapse for SiOx passivated HEMT caused by the introducing of deep traps when compared with the SiNx and SiON passivated devices. Moreover, the small-signal measurement shows that the SiON passivated HEMT has a higher cut-off frequency due to the improvement in transconductance, which makes it a promising passivation layer for GaN based high power HEMT applications.

Effects of traps in the gate stack on the small-signal RF response of III-V nanowire MOSFETs

Abstract: We present a detailed study of the effect of gate-oxide-related defects (traps) on the small-signal radio frequency (RF) response of III-V nanowire MOSFETs and find that the effects are clearly identifiable in the measured admittance parameters and in important design parameters such as h 21 (forward current gain) and MSG (maximum stable gain). We include the identified effects in a small-signal model alongside results from previous investigations of III-V RF MOSFETs and thus provide a comprehensive physical small-signal RF model for this type of transistor, which accurately describes the measured admittance parameters and gains. We verify the physical basis of the model assumptions by calculating the oxide defect density from the measured admittances.

Effect of Film Thickness and Temperature on the Resistive Switching Characteristics of the Pt/HfO2/Al2O3/TiN Structure

Abstract: Thin films with HfO2/Al2O3 laminated structure were prepared by the ALD method in this paper. Typical bipolar resistance switching characteristics were observed in the Pt/HfO2/Al2O3/TiN structure device. The samples were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The effects of dielectric thickness and different test temperatures on the electrical performance were investigated. Experiments show that when the thickness of HfO2/Al2O3 is 7 nm/3 nm, the electrical properties are the best. As the test temperature increases, the resistance values (RLRS and RHRS) of the Pt/HfO2/Al2O3/TiN structure fluctuate more and more. When the test temperature approaches the failure temperature, the device's transition voltages (VSet and VReset) will also become more volatile.

Life-time degradation of STT-MRAM by self-heating effect with TDDB model

Abstract: Spin-transfer torque magnetic random access memory (STT-MRAM) is one of the most promising candidates for “universal memory” with the ultra-fast access speed, radiation resistance and theoretically unlimited endurance. However, there are many practical aspects that could degrade the life-time of STT-MRAM. In this paper, degradation on the life-time of the STT-MTJ device is observed experimentally, which is attributed to the so-called “self-heating effect” of the device. Simulation on the device is conducted on the self-heating effect to obtain the internal temperature inside the device. The self-heating effect of the STT-MTJ device is analyzed and its influence on the life-time degradation of the STT-MTJ is included in the time dependent dielectric breakdown model (TDDB, 1/E model). This inclusion should improve the accuracy of the estimation on the life-time.