Showing papers presented at "International Meeting for Future of Electron Devices, Kansai in 2015"

Characteristics of perovskite solar cells under low illuminance condition

Abstract: In this study, we investigated the characteristics of perovskite solar cells under low illuminance condition for indoor application of perovskite solar cells. The open-circuit voltage remained around 70% at 0.1% illuminance of AM1.5. This result indicates the potential for indoor application of perovskite solar cells.

Improved current collapse in AlGaN/GaN HEMTs with 3-dimensional field plate structure

Abstract: This paper describes significantly suppressed current collapse in AlGaN/GaN HEMTs with a 3-dimensional field plate (3DFP) structure. 3DFP consists of a gate field plate deposited on a passivated SiN film and equally-spaced multiple grooves formed by dry-etching of AlGaN/GaN layers, and hence the effective field plate area has been efficiently increased. Optimizing the groove spacing of 3DFP, the device showed almost current collapse-free operation without sacrificing the drain current reduction.

Current collapse in AlGaN/GaN HEMTs with a GaN cap layer

Abstract: This paper describes electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with a GaN cap layer. The maximum drain current was kept constant at around 0.4 A/mm for a GaN cap layer thickness up to 5 nm. It was found that the degree of current collapse was gradually improved when the GaN cap thickness was increased from 0 (without cap) to 10 nm.

Terahertz resonant tunneling diode systems for next generation wireless communication

Abstract: For low cost and short distance wireless data communication systems in the THz frequency range, resonant tunneling diodes (RTDs) are very promising. To obtain a large signal-to-noise ratio, thus high data rate, the transmitter output power and receiver sensitivity have to be high. In this paper, we discuss how to overcome the limitations of current RTD-based systems for wireless communication with respect to circuit design, showing our latest experimental results.

High drain current and low on-resistance in AlGaN/GaN HEMTs with Au-plated ohmic electrodes

Abstract: This paper describes the effect of thickening Au-plated ohmic electrodes in AlGaN/GaN HEMTs on the drain current and on-resistance. By increasing the thickness of Au-plated ohmic electrodes up to 5 µm, the fabricated AlGaN/GaN HEMT with a total gate width from 2 to 10 mm exhibited an increase in the maximum drain current by about 50 % and a reduction in the on-resistance by more than 40 %.

Nano-channel InAlN/GaN Fin-HEMTs for ultra-high-speed electronics

Abstract: A stress engineered nano-channel (NC) In 0.17 Al 0.83 N/GaN T-gate Fin-High-Electron-Mobility Transistor (Fin-HEMT) exhibited a very high I Dmax of >3900 mA/mm, a highest g m of >1410 mS/mm and V th of −3.31 V at V D = 6V with good pinch-off characteristics. This dramatic increase of I D , g m and extracted electron velocity (ν e ) of 6.0×107 cm/s in the In 0.17 Al 0.83 N/GaN NC Fin-HEMT is due to the tensile stress by T-shape gate and SiN passivation. The Fin-HEMTs were also exhibited impressive device performance (g m =646 mS/mm, I on =1.03 A/mm, I OFF =1.13 µA/mm, I ON /I OFF ∼106, SS=82 mV/dec) even at V D of 0.5 V.

Low drift MEMS humidity sensor by intermittent heating

Abstract: Polymer capacitive humidity sensor with micro heater was fabricated by MEMS (Micro Electro Mechanical Systems) technique. The most suitable input power which can achieve high precision and the low consumption was found. It was demonstrated that intermittent heating of humidity sensitive material reduced the drift at high humidity. This MEMS humidity sensor would be a technology suitable for the applications which require the precision in high humidity with small size and low power consumption.

III–V/Ge MOSFETs and tunneling FETs on Si platform for low power logic applications

Abstract: CMOS utilizing high mobility III–V/Ge channels on Si substrates is expected to be one of the promising devices for low power advanced LSIs in the future, because of the expectation of high current drive. In addition, Tunneling-FET (TFET) using III–V/Ge-based materials can also be one of the important device families with steep slope device switching, which is mandatory for the ultra-low power devices. In this paper, we address the device engineering of III–V/Ge channel formation, low resistivity source/drain (S/D) with steep profile and MOS gate stacks for realizing these devices, compatible with the Si platform.

1.2kW power combiner unit using phase control for 2.4GHz band

Abstract: The microwave power source is widely used for heating and dryness, etc. so far. To solve problem (high voltage and short life time, difficult control) of the magnetron used now, semiconductor (GaN-HEMT, LDMOS) is examined. It is necessary to combine several modules to get 1kW, because the output power of semiconductor devices is about 200W. When output power and phase of each module are different, we analyzed the combined output power. We achieved 1.2kW output power by controlling the output of each module.

Countermeasure of TWINE against power analysis attack

Abstract: Lightweight block ciphers, which can be embedded using small area, have attracted much attention. This study proposes a new countermeasure for TWINE which is one of the most popular light weight block ciphers. The proposed method masks the correlation between power consumption and confidential information by adding random numbers to intermediate data of encryption. Experiments prove effective tamper-resistance of the proposed method.

CMOS circuits and nanodevices for spike based neural computing

Abstract: This paper describes hardware implementation of two integrate-and-fire type neuron models for spike based computing: pulse-coupled phase oscillator networks and spiking neural networks. A coupled Markov random field model for image region segmentation can be implemented using a pulse-coupled phase oscillator network. Multiply-and-accumulation calculation can be performed using rise timing of responses in an integrate-and-fire type spiking neuron model. Both oscillator and neuron models can be implemented by CMOS circuits consisting of capacitors with current sources or resistors. For constructing large-scale networks, nanodisk array structures are used for realizing high resistance.

Evaluation of band structure and conductive property of iron pyrite (FeS 2 ) thin film deposited by spin-coating

Abstract: Iron pyrite, FeS 2 is a semiconductor that has attention as next generation material for solar cells. We reported the evaluation of band structure and the conductivity of FeS 2 thin film toward a realization of FeS 2 heterojunction solar cells. FeS 2 thin film was prepared by spin-coating. The pyridine solution which included Iron(III) acetylacetonate was utilized as a precursor ink and the precursor film was deposited on non-alkali glass by spin-coating. The deposited film were prebaked in air at 320°C for 15 min and annealed in sulfur gas for 60 min. The ionization potential, the Fermi level, and the bandgap were measured by PYS, valence band spectrum using XPS, and UV-Visible light transmission, respectively. In addition, the resistivity of the prepared thin film was also evaluated.

A simulation study on soft error rate in STT-MRAM

Abstract: Using a three-dimensional device simulator, we evaluate the single event upset probability of spin-transfer torque magnetic random access memory (STT-MRAM) supposing various radiation conditions such as linear energy transfer and incident direction. It is shown that STT-MRAM has enough tolerance for the radiation on the ground considering typical MTJ parameters for the present MRAM technology.

AlGaAs/InGaAs HEMTs passivated with atomic layer deposited SiO 2 using aminosilane precursors

Abstract: Atomic layer deposited SiO 2 has been applied to AlGaAs/InGaAs high electron mobility transistors (HEMTs) for surface passivation employing bis(ethylmethylamino)silane (BEMAS) and tris(dimethylamino)silane (3DMAS). The BEMAS SiO 2 HEMT has achieved a lower on-resistance, as compared to the 3DMAS. This suggests excellent termination of surface dangling bonds by BEMAS.

Photo-excited carrier transport of CuPc/C 60 organic thin-film solar cells

Abstract: We prepare copper phthalocyanine (CuPc)/C 60 -based organic thin-film solar cells and investigate photo-excited carrier lifetime to reveal the carrier transport dynamics of the solar cells. The photo-excited carrier was generated by irradiation of pulsed laser light of Nd-YAG laser. The obtained carrier lifetime is much longer than that of estimated lifetime from the mobility of thin-film layers. This means the carrier transport cannot be described by a general carrier drift model. In addition, the carrier lifetime become short under white halogen light illumination. The results suggest that the trapping levels exist in organic layers..

Neuron MOS inverter and source follower using thin-film transistors

Abstract: We have developed neuron MOS devices using TFTs. We fabricated and evaluated neuron MOS inverter, which can be also utilized as a variable threshold voltage inverter, and neuron MOS source follower, which can be also utilized as a digital-analog converter. The neuron MOS devices indicate that TFTs have great potential for application to artificial neural networks.

Simulation study of NO 2 -exposed H-terminated diamond FETs with Al 2 O 3 insulator gate

Abstract: This paper investigated the simulation model for NO 2 -exposed H-terminated diamond FETs with Al 2 O 3 insulator gate, which have very good DC/RF characteristics and thermally stable operation. The NO 2 adsorption and H terminated layer were replaced to fixed charges at the interface between the Al 2 O 3 insulator and diamond. The simulation results agreed qualitatively with the experimental data. The formation of the two dimensional hole gas at on-state was confirmed at on-state. Moreover, drain current response was calculated for sinusoidal input of the gate electrode.

Discrete-type 24GHz SPDT FET switch for millimeter-wave WiCoPT

Abstract: SPDT switch for 24GHz WiCoPT system was developed. GaAs HJ-FET molded in plastic package is used for cost reduction. In this case, electrical length between drain and source, and parasitic capacitance of package cannot be neglected. To solve this problem, quarter-wavelength transmission line is inserted in series to the transistor between output port and ground port. Although switching logic is reversed, effects of the length and the parasitic capacitance are included in the transmission line. Experimental SPDT switch was fabricated to compare the performance with that of conventional one. Insertion loss of 2.9dB, attenuation of 30.5dB and isolation of 26.5dB were obtained. Amazingly, insertion loss was improved by 1.4dB and attenuation was improved by 21dB. Thus, the effectiveness of the proposed circuit was confirmed.

Vibration mode analysis on piezoelectric diaphragms for ultrasonic microsensors

Abstract: Piezoelectric diaphragm-type ultrasonic microsensors were fabricated and their vibration modes were investigated from the viewpoint of sensitivity affected by the distribution of piezoelectrically induced polarization. Three kinds of diaphragms were fabricated with the geometries of square-flat, square-buckled and circular-buckled, to clarify the effect of the diaphragm geometry to higher-order vibrations generated by a received ultrasound pulse. The square-flat diaphragms showed less higher-order vibrations compared to the square-buckled ones, and the circular-buckled showed even less higher-order vibration among them and is the suitable geometry for the piezoelectric diaphragm sensors.

Electrical characterization of GaAs/GaAs bonding interfaces

Abstract: The electrical properties of GaAs/GaAs junctions fabricated by using surface-activated bonding (SAB) were investigated. We extracted the potential barrier heights at 300-°C-annealed GaAs/GaAs interfaces from their current-voltage characteristics measured at varied ambient temperatures and estimated the energy of charge neutral level E CNL and the density of interface states D it .

Polarity dependent radiation hardness of GaN

Abstract: The lattice polarity dependent tolerance of displacement damage was studied for GaN by irradiating its +c and −c surfaces with a proton beam of 8 MeV. In agreement with the in-situ monitored increase of electrical resistance during irradiation, post-irradiation analysis by positron annihilation measurement revealed that the +c surface had a higher tolerance compared with that of the −c one. These results indicate that the defect introduction rate depends on the incident axis of proton beams.

Cu/Al/Mo/Au and Ni/Al/Mo/Au ohmic contacts for AlGaN/GaN heterostructures

Abstract: In this paper, the effect of thermal expansion in ohmic metals during ohmic annealing was studied to understand the mechanism of n-type ohmic formation in AlGaN/GaN heterostructures. We measured ohmic contact resistance as a function of annealing temperature for metal stacks composed of Cu/Al/Mo/Au, Ni/Al/Mo/Au, and Ti/Al/Mo/Au. Specific contact resistivity values of lower than 10−5 Ωcm2 were, for the first time, achieved for both Cu/Al/Mo/Au and Ni/Al/Mo/Au. The minimum contact resistance for Cu/Al/Mo/Au, Ni/Al/Mo/Au, and Ti/Al/Mo/Au were 0.36 Ωmm, 0.39 Ωmm, and 0.26 Ωmm, respectively.

Fabrication of the solar-blind photodetector based on Ni x Mg 1−x O films by radio-frequency sputtering

Abstract: Solar-blind photodetectors are fabricated with Ni x Mg 1−x O films that are formed on MgO single crystal substrate using a simple RF sputtering technique and a Ni-Mg composite target. The optical bandgap increases from 3.61 to 3.95eV as the Ni concentration decreases from 1 to 0.52. Photoconductors with interdigitated electrodes are fabricated using the sputtered Ni x Mg 1−x O films. The device based on Ni 0.52 Mg 0.48 O exhibits a peak response at a wavelength of 270nm with a cutoff wavelength of 295nm. The peak and the cutoff wavelengths of responsivity shift toward shorter wavelengths with decreasing Ni concentration.

A potentiometric glucose sensing by an enzyme-modified Ta 2 O 5 /ZnO/Zn 0.6 Mg 0.4 O solution-gate field-effect transistor

Abstract: Growth of a sputtered Ta 2 O 5 /ZnO/Zn 0.6 Mg 0.4 O film on a glass substrate and its application to an enzyme-modified field-effect transistor (EnFET) for glucose sensing are reported. This potentiometric glucose sensor showed a stable sensitivity to a wide range of glucose in an electrolyte solution with a detection response time constant of 3 s.

Design of harmonic processing circuit for microwave GaN-HEMT power amplifier

Abstract: By processing harmonics, high-efficiency microwave GaN power amplifier can be realized. However, due to parasitic elements of transistor and package, performance of actual amplifier cannot be that of ideal, especially for high power transistor. Thus, it is difficult to obtain high efficiency by ideal harmonic processing, such as class-F. Optimum harmonic reflection phases, which were different from those of class-F or inverse class-F, were calculated by harmonic balance analysis using non-linear transistor model developed by the authors. By using the model, experimental high-efficiency power amplifiers were designed and fabricated. Measured results were compared with simulated ones. As a result, effectiveness of the design method for harmonic processing amplifier using nonlinear model was confirmed.

Impacts of orientation and cross-sectional shape on hole mobility of Si nanowire MOSFETs

Abstract: We fabricated 〈100〉, 〈110〉, 〈111〉, and 〈112〉 p-channel gate-all-around Si nanowire (SiNW) MOSFETs, cross sections of which are rectangles with various widths, and investigated the hole mobility of the SiNW MOSFETs using the double L m method. Measured hole mobilities of SiNW MOSFETs were about 80–140 cm2/Vs at surface carrier density of 1 × 1013 cm−2. The dependences of the hole mobility on orientations and cross-sectional shapes of nanowires were analyzed. The orientation and geometry dependences can be explained by the band structures calculated by tight-binding approximation.

Characteristic analysis of thin-film phototransistors

Abstract: We have evaluated characteristic deviation and characteristic degradation of poly-Si thin-film phototransistors. We found that the characteristic deviation is not negligible, which seems due to energy distribution of excimer-laser crystallization, and must be compensated for some applications. We found that the characteristic degradation is negligible, which is convenient for abovementioned applications.

Macromodeling of operational amplifiers for overdrive circuit design

Abstract: This paper describes macromodeling of operational amplifiers for overdrive circuit design. Macromodels have been applied to operational amplifier simulations with good convergence. Also, macromodels allow the accurate simulation with not only double-power supply but also single-power supply. In this study, a macromodel has been applied to an overdrive circuit for sound effect design. Output waveform using the macromodel is compared with that using a pre-set model only with double-power supply and experiment. The output of the macromodel shows more accurate in amplitude, a frequency, and distortion than that of the pre-set model. From this result, the macromodel of the operational amplifier is suitable than the pre-set model in the overdrive circuit design.

High breakdown voltage AlGaN/GaN HEMTs on free-standing GaN substrate

Abstract: In this paper we have investigated the relationship between off-state breakdown voltage and gate-to-drain distance (Lgd) for AlGaN/GaN HEMTs fabricated on a free-standing GaN substrate. The off-state breakdown voltage exhibited a linear increase up to Lgd of around 80 µm but saturated at about 4000 V when Lgd > 80 µm. Therefore, we proposed that when Lgd 80 µm, it was determined by the leakage current outside of the channel.

Evolution of nanoscale silicon CMOS technology for ultra low power application

Abstract: Nanoscale silicon CMOS technology aimed for ultra low power application is presented. The characteristics variability and noise of FinFETs are dramatically suppressed by introducing an amorphous metal gate, and the suppression is beneficial both for scaling and reduction of power consumption. A tunnel FET (TFET) is also promising candidate to reduce the power consumption dramatically. The current drivability of a silicon TFET is improved significantly by introduction of a fin-type 3D structure and novel trap engineering.