Monthly Archives: September 2014

Hysteresis and threshold switching characteristics in thin-film-transistors with inserted Pt-Fe 2 O 3 core?shell nanocrystals

Hysteresis and threshold switching characteristics were investigated in the indium-gallium-zinc-oxide (IGZO) thin-film-transistors (TFTs) with inserted Pt-Fe 2 O 3 core?shell nanocrystals (NCs) layer between source/drain and IGZO channel. The output curves showed the hysteresis with threshold drain voltage and the transfer curves showed the hysteresis with the shift of threshold gate voltage. These hysteresis, threshold switching, and shift of threshold voltage in both output and transfer curves are caused by charging of inserted NCs. These unique features demonstrated the memory and on/off switching operation by controlling both threshold gate and drain voltages through charging NCs.

Hysteresis and threshold switching characteristics in thin-film-transistors with inserted Pt-Fe 2 O 3 core–shell nanocrystals

Hysteresis and threshold switching characteristics were investigated in the indium-gallium-zinc-oxide (IGZO) thin-film-transistors (TFTs) with inserted Pt-Fe 2 O 3 core–shell nanocrystals (NCs) layer between source/drain and IGZO channel. The output curves showed the hysteresis with threshold drain voltage and the transfer curves showed the hysteresis with the shift of threshold gate voltage. These hysteresis, threshold switching, and shift of threshold voltage in both output and transfer curves are caused by charging of inserted NCs. These unique features demonstrated the memory and on/off switching operation by controlling both threshold gate and drain voltages through charging NCs.

Integration of a-IGZO Thin-Film Transistor and Crystalline-Si Interdigitated Back Contact Photovoltaic Cell With 3D Stacking Structure as Self-Powered Solar Switch

In this letter, a Ta2O5/a-IGZO thin film transistor (TFT) was directly stacked on a crystalline-Si interdigitated back contact (IBC) photovoltaic (PV) cell to create a self-powered solar switch. The a-IGZO TFT and IBC PV cell were integrated into a single chip without an external circuit. This device exhibits switching property induced by illumination. The results show that it can be switched even under a low solar illumination of 300 W/m (^{mathrm {mathbf {2}}}) due to the low threshold voltage of the a-IGZO TFT (0.25 V). The ON/OFF current contrast ratio was measured to be (sim 20) under 1-sun illumination. The fabrication process and characteristics of this device make it suitable and practicable for use as a self-powered solar switch.

High-Mobility InGaZnO TFTs Using Atmospheric Pressure Plasma Jet Technique and 248-nm Excimer Laser Annealing

With the advantages of low apparatus cost, better suitability for large-scale fabrication, and low thermal budget, the nonvacuum atmospheric pressure plasma jet technique and 248-nm excimer laser annealing were employed for the fabrication of indium gallium zinc oxide (InGaZnO) thin-film transistors. Devices with a 150-mJ/cm (^{2}) laser demonstrated excellent electrical characteristics with reduced OFF-current, including a high channel mobility of 21.2 cm (^{2}) /V-s, the ON-OFF current ratio of (7times 10^{5}) , and a subthreshold swing of 0.48 V/decade. The improvements are attributed to the increase of oxygen vacancies in the InGaZnO channel and the reduction of traps at the ZrO2/InGaZnO interface and InGaZnO bulk.

InGaZnO metal-base transistor with high current gain

The fabrication of metal-base transistors (MBTs) based on InGaZnO at room temperature is reported for the first time. With a suitable oxygen doping to the sputtering-deposited InGaZnO film and an HfSiO interlayer, improved diode performances with enhanced Schottky barrier heights of 0.70 and 0.66 eV are obtained for the base/collector (Ti/ InGaZnO) and base/emitter (Au/HfSiO/InGaZnO) junctions, respectively. InGaZnO MBT using a Ti(10 nm)/Au(10 m)/HfSiO(5 nm) dual metal base shows a high common-emitter current gain (β) 840- 310 at VCE = 2 V and IB ranging from 1 to 10 nA.

13 mW 80 GHz down-conversion mixer with 1.5 dB gain and 49.2 dB LO-RF isolation

An 80 GHz double-balanced down-conversion mixer for automotive radars using standard 90 nm complementary metal oxide semiconductor (CMOS) technology is reported. The mixer comprises a double-balanced Gilbert cell with inductive source-degeneration radio-frequency (RF) transconductance stage for wideband RF-port input impedance matching and conversion gain (CG) enhancement, a Marchand balun for converting the single RF input signal to differential signal, aMarchand balun for converting the single local oscillator (LO) input signal to differential signal and a baseband amplifier. The mixer consumes 13 mW and achieves excellent RF-port input reflection coefficient of -13.1~ -19.4 dB and LO-port input reflection coefficient of -9.1~-11.8 dB for frequencies in the range 75-85 GHz. In addition, for frequencies of 75-85 GHz, the mixer achieves CG of -1 ~1.5 dB, LO-RF isolation of 43.5-49.2 dB and LO-intermediate frequency (IF) isolation of 56.5-64.5 dB, one of the best CG and port-to-port isolation results ever reported for a CMOS down-conversion mixer with operation frequency about 80 GHz

In situ preparation, electrical and surface analytical characterization of pentacene thin film transistors

The fabrication of organic thin film transistors with highly reproducible characteristics presents a very challenging task. We have prepared and analyzed model pentacene thin film transistors under ultra-high vacuum conditions, employing surface analytical tools and methods. Intentionally contaminating the gold contacts and SiO2 channel area with carbon through repeated adsorption, dissociation, and desorption of pentacene proved to be very advantageous in the creation of devices with stable and reproducible parameters. We mainly focused on the device properties, such as mobility and threshold voltage, as a function of film morphology and preparation temperature. At 300 K, pentacene displays Stranski-Krastanov growth, whereas at 200 K fine-grained, layer-like film growth takes place, which predominantly influences the threshold voltage. Temperature dependent mobility measurements demonstrate good agreement with the established multiple trapping and release model, which in turn indicates a predominant concentration of shallow traps in the crystal grains and at the oxide-semiconductor interface. Mobility and threshold voltage measurements as a function of coverage reveal that up to four full monolayers contribute to the overall charge transport. A significant influence on the effective mobility also stems from the access resistance at the gold contact-semiconductor interface, which is again strongly influenced by the temperature dependent, characteristic film growth mode.

Room temperature deposition of high figure of merit Al-doped zinc oxide by pulsed-direct current magnetron sputtering: Influence of energetic negative ion bombardment on film’s optoelectronic properties

Publication date: 31 October 2014 Source:Thin Solid Films, Volume 569 Author(s): F. Fumagalli , J. Martí-Rujas , F. Di Fonzo Aluminum-doped zinc oxide is regarded as a promising indium-free transparent conductive oxide for photovoltaic and transparent electronics. In this study high transmittance (up to 90,6%) and low resistivity (down to 8,4°1−4 Ωcm) AZO films were fabricated at room temperature on thermoplastic and soda-lime glass substrates by means of pulsed-DC magnetron sputtering in argon gas. Morphological, optical and electrical film properties were characterized using scanning electron microscopy, UV–vis–nIR photo-spectrometer, X-ray spectroscopy and four probes method. Optimal deposition conditions were found to be strongly related to substrate position. The dependence of functional properties on substrate off-axis position was investigated and correlated to the angular distributions of negative ions fluxes emerging from the plasma discharge. Figure of merit as high as 2,15±0,14Ω−1 were obtained outside the negative oxygen ions confinement region. Combination of high quality AZO films deposited on flexible polymers substrates by means of a solid and scalable fabrication technique is of interest for application in cost-effective optoelectrical devices, organic photovoltaics and polymer based electronics.

Solution processed white light photodetector based N, N′-di (2-ethylhexyl)-3,4,9,10-perylene diimide thin film phototransistor

Publication date: 31 October 2014 Source:Thin Solid Films, Volume 569 Author(s): Cem Tozlu , Mahmut Kus , Mustafa Can , Mustafa Ersöz In this study, a solution-processed n-type photo-sensing organic thin film transistor was investigated using polymeric dielectric under different white light illuminations. N, N′-di (2-ethylhexyl)-3,4,9,10-perylene diimide and divinyl tetramethyl disiloxane-bis (benzo-cyclobutene) were used as a soluble active organic semiconductor and as a dielectric material, respectively. Stable amplification was observed in the visible region without gate bias by the device. The electrical characterization results showed that an n-type phototransistor with a saturated electron mobility of 0.6×10−3 cm2/V·s and a threshold voltage of 1.8V was obtained. The charge carrier density of the channel of the device exhibited photo-induced behaviors that strongly affected the electrical properties of the transistor. The photosensitivity and photoresponsivity values of the device were 63.82 and 24mA/W, respectively. These findings indicate that perylene diimide is a promising material for use on organic based phototransistors.

Transparent, High-Performance Thin-Film Transistors with an InGaZnO/Aligned-SnO2-Nanowire Composite and their Application in Photodetectors

A high mobility of 109.0 cm2 V−1 s−1 is obtained by thin-film transistors (TFTs) comprising a composite made by aligning SnO2 nanowires (NWs) in amorphous InGaZnO (a-IGZO) thin films. This composite TFT reaches an on-current density of 61.4 μA μm−1 with a 10-μm channel length. Its performance surpasses that of single-crystalline InGaZnO and is comparable to polycrystalline silicon.