Good Bias Stability Research Articles

Bilayer Metal Oxide Channel Thin Film Transistor With Flat Interface Based on Smooth Transparent Nanopaper Substrate

With the rapid development of electronic devices, a lot of electronic waste is generated yearly. They posed sereve environmental concerns. Integrating sustainable materials into electronic devices is one of promising solutions to achieve the balance between technological development and ecological protection. Cellulose nanopaper has emerged as a hot sustainable material for thin film transistors (TFT) in the flexible display. However, the performance of nanopaper TFT is generally poor. In this study, a transparent nanopaper with a root-mean-square surface roughness of 3.49 nm is prepared by spin coating cellulose nanofibrils on glass and applied as a substrate for metal oxide TFTs. Bilayer channel (IGZO/Al <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{2}}\text{O}_{{3}}$ </tex-math></inline-formula> ) TFTs with bottom gate structure are then deposited on transparent nanopaper by physical vapor deposition at room temperature. Consequently, the as-prepared nanopaper TFT not only exhibits a saturation mobility of as high as 21.98 cm2/(V·s), an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{\text {on}}/\text{I}_{\text {off}}$ </tex-math></inline-formula> ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${5.07}\times {10} ^{{6}}$ </tex-math></inline-formula> , and a subthreshold swing of 0.75 V/dec, but shows good bias stability. This work brings a step closer to green, sustainable, and inexpensive transparent paper electronics.

Dimensional structure regulation of organic–inorganic hybrid perovskite and its application in thin film transistors

The effects of dimensional structure on the properties of lead iodide perovskite (C8H9NH3)2(CH3NH3) n−1Pb n I3n+1 were investigated. Furthermore, perovskite thin films with different dimensionalities were applied as the channel layer of thin film transistors (TFT). The electrical performance and stability of TFT devices were significantly improved through the regulation of dimensional microstructure of the perovskites. As a result, the quasi-2D (n = 6) perovskite TFTs achieved a field-effect mobility (μ FE) of 3.90 cm2 V−1 s−1, with 104 on-off current ratio and −1.85 V threshold voltage, which can be maintained well after 4 days without degradation at 30% ambient humidity. Moreover, the electrical performance of the TFTs based on Pure-2D and Quasi-2D perovskite also exhibited a good bias stability.

Yttrium Doped Copper (II) Oxide Hole Transport Material as Efficient Thin Film Transistor.

This work reports development of yttrium doped copper oxide (Y-CuO) as a new hole transport material with supplemented optoelectronic character. The pure and Y-doped CuO thin films are developed through a solid-state method at 200 °C and recognized as high performance p-channel inorganic thin-film transistors (TFTs). CuO is formed by oxidative decomposition of copper acetylacetonate, yielding 100 nm thick and conductive (40.9 S cm-1 ) compact films with a band gap of 2.47 eV and charge carrier density of ∼1.44×1019 cm-3 . Yttrium doping generates denser films, Cu2 Y2 O5 phase in the lattice, with a wide band gap of 2.63 eV. The electrical conductivity increases nine-fold on 2 % Y addition to CuO, and the carrier density increases to 2.97×1021 cm-3 , the highest reported so far. The TFT devices perform remarkably with high field-effect mobility (μsat ) of 3.45 cm2 V-1 s-1 and 5.3 cm2 V-1 s-1 , and considerably high current-on/off ratios of 0.11×104 and 9.21×104 , for CuO and Y-CuO films, respectively (at -1 V operating voltage). A very small width hysteresis, 0.01 V for CuO and 1.92 V for 1 % Y-CuO, depict good bias stability. Both the devices work in enhancement mode with stable output characteristics for multiple forward sweeps (5 to -60 V) at -1Vg .

An Active Multielectrode Array for Collecting Surface Electromyogram Signals Using a-IGZO TFT Technology on Polyimide Substrate

The surface electromyogram (sEMG) signals produced by living bodies play a significant role in biological applications. However, an active multielectrode array (MEA) having a high spatiotemporal resolution, flexibility, and high gain is still an enormous challenge for accurate sEMG detection. Here, a flexible active MEA based on the diode-connected load inverter is proposed and fabricated for collecting sEMG signals using amorphous indium&#x2013;gallium&#x2013;zinc oxide (a-IGZO) thin-film transistors (TFTs) technology on the polyimide (PI) substrate. To obtain the good gain effect and low-noise active MEA, the width&#x2013;length ratio of the transistors and the suitable impedances are systemically designed. Moreover, the optimized circuit exhibits good bias stability, excellent uniformity in electrical performance, and outstanding mechanical durability, which can ensure reliable sEMG detection. With the combination of the a-IGZO TFTs, the active MEA has an approximate 15-dB signal gain under a low driving voltage of 5 V. Measuring the sEMG of the muscle groups below the thumb with our developed flexible active MEA, the amplitude value of sEMG signals is successfully amplified and the noise fluctuation is obviously reduced. Thus, the active MEA has certain advantages in large-area preparation, stability, flexibility, and high gain, which opens a new avenue for the accurate sEMG signal measurements.

Design and Fabrication of a Slanted-Beam MEMS Accelerometer

This paper presents a novel capacitive microelectromechanical systems (MEMS) accelerometer with slanted supporting beams and all-silicon sandwich structure. Its sensing mechanism is quite similar to an ordinary sandwich-type MEMS accelerometer, except that its proof mass is suspended by a beam parallel to the {111} plane of a (100) silicon wafer. In this way, each sensing element can detect accelerations in two orthogonal directions. Four of these sensing elements could work together and constitute a 3-axis micro-accelerometer by using a simple planar assembly process. This design avoids the traditional 3-axis accelerometer’ disadvantage of possible placement inaccuracy when assembling on three different planes and largely reduces the package volume. The slanted-beam accelerometer’s performance was modeled and analyzed by using both analytical calculations and finite element method (FEM) simulations. A prototype of one sensing element was fabricated and tested. Measured results show that this accelerometer has a good bias stability 76.8 ppm (1σ, tested immediately after power on), two directional sensitivities (sensitivity angle α = 45.4°) and low nonlinearity (<0.5%) over a sensing range up to ±50 g, which demonstrates a great opportunity for future high-precision three-axis inertial measurement.

Bottom-Gate Self-Aligned Homojunction TFT with Double Oxide Semiconducting Layers

After huge effort has been made over the last decade, oxide thin-film transistors (TFTs) have been successfully adopted in the backplane of high resolution AM-LCD and AM-OLED displays. However, as displays and electronic devices evolve to next generations, it is necessary to not only enhance field-effect mobility, but also reduce RC-delay for high driving speed [1, 2]. In this regard, self-aligned structure has been considered as one of promising candidates for satisfying these requirements [3] due to the minimum parasitic capacitances between electrodes. Nonetheless, there are several concerns especially in doping process at contact region because it is difficult to control dopant diffusion, resulting in unstable performance and another unexpected parasitic capacitance. Here, we propose improved structure adopting double oxide semiconducting layers, which can precisely define the channel dimension by gate electrode. Figure 1 demonstrates both structures of conventional self-aligned TFT and our improved self-aligned TFT. As shown in the figure, first channel layer of oxide material with high mobility and high carrier density plays as the real electron flow path and the contacts with source/drain (S/D) metal electrode without additional doping process. Consequently, the issues originated from doping process can be easily overcome. Meanwhile, second active layer with the relatively low carrier density is defined by the gate electrode and plays a role as a carrier controlling part for reliable switching performance. To fabricate our self-aligned TFTs, gate metal was firstly patterned on glass substrate by wet etching. After depositing SiO2 by PECVD as a gate insulator, first semiconducting layer was grown by sputter or plasma-enhanced atomic layer deposition (PEALD). The second active layer was deposited and formed by back-side exposure using gate electrode as a masking layer. Then, SiO2 by PECVD was deposited to passivate whole device. Finally, S/D metal layer was formed, followed by annealing process in vacuum condition. As a starting research, we had to carefully consider proper oxide semiconductors according to their characteristics and etch selectivity between first and second channel layers. Although adopting highly conducting oxides such as ITO and In2O3 as a first channel layer would be better for lowering the contact resistance, it is hard to deplete the carriers. Hence, thinner film thickness (<10nm) or other deposition method such as PEALD should be considered to obtain semiconducting behavior. Accordingly, we have firstly investigated the switching behavior of In2O3/ZnO double layered TFT by means of PEALD with bottom-gate coplanar structure. The In2O3/ZnO TFT shows mobility of 32 cm2/Vs with good bias stability as shown in Figure 2. The improved self-aligned TFTs were successfully fabricated and well-performed using sputtered ITO/IGZO and PEALD In2O3/ZnO. We will report the device characteristics and further investigate and reveal the origin of stable electrical behavior by simulation. [Acknowledgement] This work was supported by Open Innovation Lab Project from National Nanofab Center (NNFC). [Reference] [1] K. Yokoyama, S. Hirakata, S. Yamazaki, M. Nakada, T. Sato, and N. Goto, “A 2.78-in 1058-ppi ultra-high-resolution OLED display using CAAC-OS FETs,” SID digest 2015, 46, 1039-1042. [2] J. U. Bae, D. H. Kim, K. Kim, K. Jung, W. Shin, I. Kang, and S. D. Yeo, “Development of oxide TFT’s structures,” SID digest 2013, 44, 89-92. [3] N. Morosawa, Y. Ohshima, M. Morooka, T. Arai, and T. Sasaoka, “Novel self-aligned top-gate oxide TFT for AMOLED displays,” Journal of the society for Information Display 2012, 20 (1), 47-52. Figure 1

Airborne gravimetry for geoid determination with Lacoste Romberg and Chekan gravimeters

Airborne gravimetry for geodetic purposes such as geoid determination and global geopotential models requires good bias stability, as well as good performance in turbulence for large-scale national projects. DTU-Space has since many years carried out large area airborne surveys over polar, tropical and temperate regions. Recently we have started flying two gravimeters (L&R and Chekan-AM) side by side for increased reliability and redundancy in several surveys. In the paper we will give some examples of recent survey results, confirming accuracies in the 1 mGal range for a well-controlled Danish flight test, and around 3 mGal for intercomparisons of Chekan and L&R results in Nepal, one of the most challenging field survey regions on the Earth. We also indicate the good agreement between airborne gravity and GOCE data in Nepal, and outline the use for improved geoid determination.

Characterization of novel BaZnSnO thin films by solution process and applications in thin film transistors

A novel BaZnSnO semiconductor is fabricated using solution process and the influence of Ba addition on the structure, the chemical state of oxygen and electrical performance of BaZnSnO thin films are investigated. A high performance BaZnSnO-based thin film transistor with 15mol% Ba is obtained, showing a saturation mobility of 1.94cm2/Vs, a threshold voltage of 3.6V, an on/off current ratio of 6.2×106, a subthreshold swing of 0.94V/decade, and a good bias stability. Transistors with solution processed BaZnSnO films are promising candidates for the development of future large-area, low-cost and high-performance electronic devices.

Sputtered Deposited Carbon–Indium–Zinc Oxide Channel Layers for Use in Thin-Film Transistors

We have fabricated thin-film transistors (TFTs) using an amorphous carbon-indium-zinc oxide (a-CIZO) as an active-channel layer deposited via radio-frequency sputtering on atomic layer deposition grown Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrates at room temperature. The deposited a-CIZO TFT postannealed at 250°C exhibited a saturation field effect mobility of 32.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V · s, a subthreshold swing of 0.55 V/decade, a threshold voltage of 11.2 V, and an ON/OFF current ratio of 6.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> . Moreover, the a-CIZO TFTs showed with a good bias stability.

Overcoming tradeoff between mobility and bias stability in organic field-effect transistors according to the self-assembled monolayer chain lengths

This study examined the relationship between the mobility and bias stability of pentacene-based organic field-effect transistors (OFETs) regarding a self-assembled monolayer (SAM) treatment. For this systematic study, four types of silazane-based SAMs with different alkyl chain lengths in the range of 1–8 were used. Silazane-based SAMs have an advantage of processability due to the mild reaction conditions. The mobility was increased from 0.29 without SAM to 0.46, 0.61, 0.65, and 0.84 cm2/V s after the SAM-treatment with an alkyl chain length of 1, 3, 4, and 8, respectively. On the other hand, inverse proportional relationship was observed between the bias stability and SAM alkyl chain length. Under high gate bias stress (equivalent to electric field of 3 MV/cm) for 2 h, the threshold voltage shift of the OFET was decreased from 12.19 V without SAM to 5.69 V with a short SAM-treatment (alkyl chain length of 1) and 7.14 V with a long SAM-treatment (alkyl chain length of 8). This is the significant finding that there was a tradeoff relationship between the mobility and bias stability of OFETs concerning the SAM alkyl chain length. To overcome this tradeoff, a method for surface engineering using two-step SAM-treatment was introduced. By treating long SAM and short SAM in sequence, both the high mobility and good bias stability were achieved. With two-step SAM-treatment, the OFET showed high mobility as a long SAM-treated OFET and good bias stability as a short SAM-treated OFET.

Improving electrical performance and bias stability of HfInZnO-TFT with optimizing the channel thickness

RF magnetron sputtered HfInZnO film and atomic layer deposition (ALD) Al2O3 film were employed for thin film transistors (TFTs) as channel layer and gate insulator, respectively. To achieve HfInZnO-TFT with high performance and good bias stability, the thickness of HfInZnO active layer was optimized. The performance of HfInZnO-TFTs was found to be thickness dependent. As the HfInZnO active layer got thicker, the leakage current greatly increased from 1.73 × 10−12 to 2.54 × 10−8 A, the threshold voltage decreased from 7.4 to −4.7 V, while the subthreshold swing varied from 0.41 to 1.07 V/decade. Overall, the HfInZnO film showed superior performance, such as saturation mobility of 6.4 cm2/V s, threshold voltage of 4.2 V, subthreshold swing of 0.43 V/decade, on/off current ratio of 3 × 107 and Vth shift of 3.6 V under VGS = 10 V for 7200 s. The results demonstrate the possibility of fabricating TFTs using HfInZnO film as active layer and using ALD Al2O3 as gate insulator.

Transparent Flexible Circuits Based on Amorphous-Indium–Gallium–Zinc–Oxide Thin-Film Transistors

Circuits implemented with high-performance amorphous-indium-gallium-zinc-oxide thin-film transistors (TFTs) are realized on polyimide/polyethylene-terephthalate plastic substrates. The TFTs on plastic exhibit a saturation mobility of 19 cm2/V·s and a gate voltage swing of ~0.14 V/dec. For an input of 20 V, an 11-stage ring oscillator operates at 94.8 kHz with a propagation delay time of 0.48 μs. A shift register, consisting of ten TFTs and one capacitor, operates well with good bias stability. AC driving of pull-down TFTs gives the gate driver an improved lifetime of over ten years.

Annealing and Composition Effects of (BaxSr1-x)Ta2O6 Thin Films Fabricated by Sol–Gel Method

The annealing atmosphere effects and composition effects on the electrical properties of five compositions of (BaxSr1-x)Ta2O6 thin films were investigated. O2 atmosphere annealing prevented the diffusion of Ti from the substrates into thin films and thus improved the dielectric properties of thin films. Thin films of all compositions show dielectric constants higher than 60 and loss tangents lower than 1%. Sr substituted for Ba in BaTa2O6 thin films showed a strong influence on the material properties. Among the samples, (Ba0.75Sr0.25)Ta2O6 thin film shows good bias stability, a high dielectric constant of about 65, low loss tangent of about 0.9% and low leakage current of about 10-7 A/cm2, and is regarded as the most promising for application in next-generation miniaturization.

All DSP 기반의 비편광 FOG 설계 및 제작

The interferometric fiber optic gyroscopes (FOGs) are well known as sensors of rotation, which are based on Sagnac effect, and have been under development for a number of years to meet a wide range of performance requirements. This paper describes the development of open-loop FOG and digital signal processing techniques implemented on FPGA. Our primary goal was to obtain intermediate accuracy (pointing grade) with a good bias stability (0.22deg) and scale factor stability, extremely low angle random walk (0.07deg) and significant cost savings by using a single mode fiber. A secondary goal is to design all digital FOG signal processing algorithms with which the SNR at the digital demodulator output is enhanced substantially due to processing gain. The Cascaded integrator bomb(CIC) type of decimation filter only requires adders and shift registers, low cost processors which has low computing power still can used in this all digital FOG processor.

Darlington feedback amplifier with good bias stability under large-signal conditions

A Darlington cell using resistive biasing suffers from bias stability under large-signal conditions, which can be detrimental at radio frequencies. Replacing the resistor with a transistor in a configuration similar to a current source but acting also as an amplifier has shown a beneficial improvement.

Transient phase response of a solid state pulsed X-band source

A solid state pulsed X-band source (crystal oscillator-multiplier type) yielding low transient phase distortion and high on/off ratio is described. Design tradeoffs are discussed, and it is shown that placing the RF switch before the last frequency multiplier is a suitable compromise design. Low switch VSWR and good bias stability in the switched stages are necessary for satisfactory transient phase performance.