Gallium Zinc Oxide Research Articles

Lanthanide-doped zinc gallium oxide (ZnGa2O4) nanocrystals and their engineered photoluminescence

Lanthanide-doped zinc gallium oxide (ZnGa2O4) nanocrystals and their engineered photoluminescence

Enhancement-mode ZnGa2O4-based Phototransistor with high UV–visible rejection ratio grown by metalorganic chemical vapor deposition

In this study, a high-crystallinity zinc gallium oxide (ZnGa2O4) epilayer of about 80 nm thickness was successfully grown using metalorganic chemical vapor deposition. X-ray diffraction, atomic force microscopy, UV–visible spectroscopy measurements, and X-ray photoelectron spectroscopy were used to investigate the quality of the epilayer. Transmission line measurement analysis revealed the electrical properties of the ZnGa2O4 epilayer: a sheet resistance of 276 MΩ/□, a transfer length of 0.28 μm, and a specific contact resistivity of 21.63 Ω/mm2. A phototransistor made of ZnGa2O4 was designed with a channel width of 250 μm and a channel length of 20 μm. The source-drain electrodes were fabricated using a Ti/Al/Ni stacking technique. The gate dielectric comprised 30 nm thick Al2O3, and the gate contact was made of Ni. The device possessed a higher threshold voltage value of about 4.8 V and an impressive On/Off current ratio of 106. Under 240 nm UV light exposure, the phototransistor exhibited a transition from enhancement mode to depletion mode, leading to a remarkable shift in the threshold voltage from 5 V to approximately −16 V. Moreover, the responsivity and rejection ratio at 240 nm was 128.5 A/W and 105 at a gate voltage of −10 V. The study shows that an increasing thickness of the ZnGa2O4 epilayer from 80 nm to 135 nm results in a depletion mode transistor. The higher concentration of about twenty percent oxygen vacancies resulted in a longer fall time for the phototransistor. These results underscore the significant potential of ZnGa2O4 in facilitating deep UV-based detection applications.

A Human-Computer Interaction Strategy for An FPGA Platform Boosted Integrated "Perception-Memory" System Based on Electronic Tattoos and Memristors.

The integrated "perception-memory" system is receiving increasing attention due to its crucial applications in humanoid robots, as well as in the simulation of the human retina and brain. Here, a Field Programmable Gate Array (FPGA) platform-boosted system that enables the sensing, recognition, and memory for human-computer interaction is reported by the combination of ultra-thin Ag/Al/Paster-based electronic tattoos (AAP) and Tantalum Oxide/Indium Gallium Zinc Oxide (Ta2O5/IGZO)-based memristors. Notably, the AAP demonstrates exceptional capabilities in accommodating the strain caused by skin deformation, thanks to its unique structural design, which ensures a secure fit to the skin and enables the prolonged monitoring of physiological signals. By utilizing Ta2O5/IGZO as the functional layer, a high switching ratio is conferred to the memristor, and an integrated system for sensing, distinguishing, storing, and controlling the machine hand of multiple human physiological signals is constructed together with the AAP. Further, the proposed system implements emergency calls and smart homes using facial electromyogram signals and utilizing logical entailment to realize the control of the music interface. This innovative "perception-memory" integrated system not only serves the disabled, enhancing human-computer interaction but also provides an alternative avenue to enhance the quality of life and autonomy of individuals with disabilities.

Study of geometry effect on the performance of thin-film transistors fabricated with ZnGa2O4 epilayer grown by metalorganic chemical vapor deposition for high voltage applications

Enhancement mode thin film transistors (TFTs) having different geometries were fabricated on the Zinc gallium oxide (ZnGa2O4) epilayer grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). A field emission scanning electron microscope, atomic force microscopy, and X-ray diffraction were employed to conduct a detailed analysis of the film composition, morphology, and crystal structure. The distance between the source-to-gate and gate length was kept to be 7 μm and 3 μm in all the devices with varying gate-to-drain lengths of 10, 20, and 30 μm. Moreover, neutral beam etching technology was employed to isolate the individual devices and reduce the defects induced by plasma etching. It was found that the threshold voltage changes from 6 V to 7.6 V with the increase in source to drain length from 20 μm to 40 μm. The On/Off ratio of the devices was found to be 105, with a maximum current around 1 μA/mm. Additionally, the device breakdown voltage increased from 240 V to about 656 V with the increase in the device length. The results demonstrate the fabrication of the high breakdown voltage ZnGa2O4-based TFT and establish the co-relation of the source to drain length with the device characteristics.

Deep-ultraviolet n-ZnGa2O4/p-GaN heterojunction photodetector fabricated by pulsed laser deposition.

Zinc gallium oxide (ZnGa2O4) has attracted considerable interest in deep-ultraviolet photodetectors, due to the ultrawide bandgap, high transmittance in the ultraviolet (UV) region, and excellent environmental stability. In this study, ZnGa2O4 thin films were deposited on p-GaN epi-layers using pulsed laser deposition, resulting in improved crystalline quality. The ZnGa2O4 film exhibited a bandgap of 4.93 eV, calculated through absorption spectra. A heterojunction photodetector (PD) was constructed, demonstrating a rectification effect, an on/off ratio of 12,697 at -5.87 V, a peak responsivity of 14.5 mA/W, and a peak detectivity of 1.14 × 1012 Jones (262 nm, -6 V). The PD exhibited a fast response time (39 ms) and recovery time (30 ms) under 262 nm illumination. The band diagram based on the Anderson model elucidates the photoresponse and carrier transport mechanism. This work paves the way for advancing next-generation optoelectronics.

Deep blue emission and latent finger print detection analysis of zinc gallate nanoparticles

For the first time, Zinc Gallium Oxide is synthesized using LeucasAspera leaves extract as a reducing agent followed by the calcination at 500∘C. The structural, morphological, and optical properties are discussed. The Bragg reflections confirm that ZGO gets crystallized in pure cubic form. The surface morphology consists of agglomerated NPs. The direct energy band gap was found to be 3.1 eV. The photoluminescence analysis excited under 233 nm, and CIE values fall in the blue region of visible spectra. The CCT value was found to be 2748 K which might find an application as a nanophosphor in warm light-emitting diodes. Further, the powder dusting method was employed to collect the latent fingerprints (LFPs) on the pores and non-pores surfaces under UV as well as in day light. The synthesized ZGO exhibits well-resolved ridge patterns that can be used to identify LFPs with clarity. From all these results, the present synthesized ZGO NPs might find an application in display technology as a blue nanophosphor material and for LFP detection in crime investigation.

On-receptor computing with classical associative learning in semiconductor oxide memristors.

The increasing demand for energy-efficient data processing leads to a growing interest in neuromorphic computing that aims to emulate cerebral functions. This approach offers cost-effective and rapid parallel data processing, surpassing the limitations of the conventional von Neumann architecture. Key to this emulation is the development of memristors that mimic biological synapses. Recently, research efforts have focused on the incorporation of nociceptors-sensory neurons capable of detecting external stimuli-into memristors for applications in robotics and artificial intelligence. This integration enables memristors to adapt to various circumstances while remaining cost-effective. A nonfilamentary gradual resistive switching memristor is utilized to implement artificial nociceptor and synaptic behaviors. The fabricated Pt/indium gallium zinc oxide (IGZO)/SnOx/TiN device exhibits essential properties of biological nociceptors, including threshold response, no-adaptation, relaxation, sensitization, and recovery. Furthermore, the device leverages short-term memory principles to emulate learning behaviors observed in the brain by showcasing "forgetting" paradigms. Additionally, control of the input spikes yields different synaptic plasticity responses, thus emulating the key functions of our synapse. Computational simulations demonstrate the device's ability to perform both computing and sensing tasks effectively, thus enabling on-receptor computing with associative learning capabilities.

Deposition and photoluminescence of zinc gallium oxide thin films with varied stoichiometry made by reactive magnetron co-sputtering

This paper reports on the deposition and photoluminescence of amorphous and crystalline thin films of zinc gallium oxide with Ga:Zn atomic ratio varied between 0.3 and 5.7. The films are prepared by reactive direct current magnetron co-sputtering from liquid/solid gallium/zinc targets onto fused quartz substrates; the temperature of the substrate is varied from room temperature (RT) to 800 °C. The sputtering process is effectively controlled by fixing the sputtering power of one of the targets and controlling the power of the other target by plasma optical emission spectroscopy. The method, in conjunction with oxygen flow adjustment, enables the production of near-stoichiometric films at any temperature used. The composition analysis suggests a few at% oxygen deficiency in the films. The resulting deposition rate is at least an order of magnitude higher compared to the commonly used radio-frequency sputtering from a ceramic ZnO:Ga2O3 target. Deposited onto unheated substrates, the films with Ga:Zn ≈ 2 are X-ray amorphous. Well-defined X-ray diffraction peaks of spinel ZnGa2O4 start to appear at a substrate temperature of 300 °C. The surface of the as-deposited films is dense and exhibits a fine-featured structure observed in electron microscopy images. Increasing the deposition temperature from RT to 800 °C eliminates defects and improves crystallinity, which for the films with Ga:Zn ratio close to 2 results in an increase in the optical band gap from 4.6 eV to 5.1 eV. Room temperature photoluminescence established the main peak at 3.1 eV (400 nm); a similar peak in Ga2O3 is ascribed to oxygen-vacancy related transitions. A prominent feature around 2.9 eV (428 nm) is attributed to self-activation center of the octahedral Ga-O groups in the spinel lattice of ZnGa2O4. It was found that photoluminescence from ZnGa2O4 depends significantly on the stoichiometric ratio between Ga and Zn and the deposition/annealing temperature.

Compositional tailoring of indium-free GZO layers via plasma-enhanced atomic layer deposition for highly stable IGZO/GZO TFT

Oxide semiconductor-based thin-film transistors (TFTs) are promising candidates for display backplanes and memory device applications. To achieve high device performance and sustain the electrical properties under prolonged operation, it is important to overcome the mobility–stability trade-off in oxide TFTs. Here, we propose a bilayer-structured semiconductor stack formed by plasma-enhanced atomic layer deposition (PEALD), where an indium-free gallium zinc oxide (GZO) film is grown on top of indium gallium zinc oxide (IGZO), to be implemented in top gate devices. Applying a GZO layer (with optimum Ga to Zn ratio) between the IGZO and the gate insulator (GI) resulted in two major effects: interface engineering and band alignment modulation. While maintaining a sufficiently large field effect mobility (31.9 cm2 V−1 s−1), considerable improvements in device reliability were observed concerning positive-bias thermal stress (PBTS) and negative-bias illumination stress (NBIS) compared to TFTs incorporating IGZO single layers. This suggests that proper composition control through PEALD in the bilayer oxide semiconductor TFT may help achieve an appropriate balance between mobility and reliability.

Highly Robust Atomic Layer Deposition‐Indium Gallium Zinc Oxide Thin‐Film Transistors with Hybrid Gate Insulator Fabricated via Two‐Step Atomic Layer Process for High‐Density Integrated All‐Oxide Vertical Complementary Metal‐Oxide‐Semiconductor Applications

Highly reliable atomic layer deposition (ALD)‐derived In‐Ga‐Zn‐O thin‐film transistors with high field‐effect mobility (μFE) and hydrogen (H) resistivity are crucial for the semiconductor industry. Herein, a hybrid Al2O3 gate insulator (GI) is proposed that is designed by controlling the plasma‐enhanced ALD and thermal ALD processes in situ to demonstrate robust characteristics. A hybrid GI is applied to the top‐gate geometry of an In0.71Ga0.08Zn0.21O active layer. The optimal device exhibits exceptional electrical characteristics, including a threshold voltage of 0.37 V, μFE of 150.7 cm2 V s−1, subthreshold swing of 64.0 mV decade−1, and hysteresis of 0.02 V. It demonstrates high resistance to H annealing and reliable positive bias temperature stress, as well as changes in VTH shifts of −0.43 and 0.00 V, respectively. The excellent electrical characteristics and high robustness of the device can be attributed to the precise control of H, oxygen, and carbon species within the upper region of the hybrid GI. The achievement of robust device characteristics enables the design of a novel vertical complementary metal‐oxide‐semiconductor inverter that exhibits a voltage gain of 44.7 V V−1 and a noise margin of 87.5% at a 10 V supply voltage.

Direct hard X-ray photodetector with superior sensitivity based on ZnGa2O4 epilayer grown by metalorganic chemical vapor deposition

In this work, we have fabricated a highly sensitive direct irradiating X-ray photodetector (DXPD) based on Zinc Gallium Oxide (ZnGa2O4) epilayers with a metal-semiconductor-metal structure. The ZnGa2O4 epilayers were grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD). To test the DXPD's capabilities, we subjected it to a synchrotron hard X-ray source with an energy of 10 keV, and measured incident radiation flux ranging from 5.7✕107 to 4.6 ✕1011 counts/sec. The effect of changing the applied bias voltage on the time response of the DXPD was investigated. The sensitivity of hard XPDs was compared using gallium oxide (β-Ga2O3) epilayer grown by MOCVD. The results showed that ZnGa2O4 DXPD had approximately 104 times greater sensitivity than the β-Ga2O3 based XPD. ZnGa2O4 based detectors also exhibited remarkable sensitivity of 2.87 × 109 μC Gyair−1cm−2 for the incident flux of 5.7✕107 counts/sec at 15 V. Additionally, the sensitivity was examined in terms of applied bias and dose rate. Based on these observations, it can be concluded that ZnGa2O4 epilayers grown by MOCVD hold immense potential for use in high-performance hard XPDs.

Electrochemical generation of hydrogen peroxide from a zinc gallium oxide anode with dual active sites

Electrochemical water oxidation enables the conversion of H2O to H2O2. It holds distinct advantages to the O2 reduction reaction, which is restricted by the inefficient mass transfer and limited solubility of O2 in aqueous media. Nonetheless, most reported anodes suffer from high overpotentials (usually >1000 mV) and low selectivity. Electrolysis at high overpotentials often causes serious decomposition of peroxides and leads to declined selectivity. Herein, we report a ZnGa2O4 anode with dual active sites to improve the selectivity and resist the decomposition of peroxides. Its faradaic efficiency reaches 82% at 2.3 V versus RHE for H2O2 generation through both direct (via OH−) and indirect (via HCO3−) pathways. The percarbonate is the critical species generated through the conversion of bicarbonate at Ga-Ga dual sites. The peroxy bond is stable on the surface of the ZnGa2O4 anode, significantly improving faradaic efficiency.

Pulsed laser deposition of ZnGa2O4 thin films on Al2O3 and Si substrates for deep optoelectronic devices applications

Due to the ultra-wideband gap, high transmittance in the ultraviolet (UV) region, and excellent environmental stability, zinc gallium oxide (ZnGa2O4) has attracted considerable interest in deep-ultraviolet photodetectors. Here, ZnGa2O4 thin film was fabricated on different substrates by pulsed laser deposition with a post-annealing process under an oxygen atmosphere. It is found that the substrates have a great impact on the morphology, structure, and crystal quality of thin film. After annealing, the thin film quality has been improved. The metal–semiconductor–metal photodetector shows excellent reproducible characteristics and fast response performance, which demonstrates great potential in next-generation optoelectronic devices.

Pt/ZnGa₂O₄ Schottky Barrier Diodes Fabricated by Using Single Crystal n-ZnGa₂O₄ (111) Substrates

In this letter, we fabricated Schottky barrier diodes (SBDs) using n-type zinc gallium oxide (n-ZnGa2O4) single-crystal substrates, which were grown from the melt by the vertical gradient freeze (VGF) method. X-ray diffraction rocking curve and Laue diffraction results indicate the good crystal quality. The electrical properties of SBDs fabricated on substrates with two doping concentrations are systematically investigated. Heavily-doped (HD) SBDs exhibit lower differential specific on-resistance (~1.13 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm2) and lower turn-on voltage (~0.16 V) while the lightly-doped (LD) SBDs exhibit better ideality factor (1.17), rectification characteristics (on/off ratio ~1011) and lower reverse leakage. In addition, we separately tested the electrical properties of the two devices at different temperatures (298 K-473 K). The results of varying temperature show that LD-SBDs have better temperature stability in smaller variation of ideality factor and barrier height with temperature. Based on these experimental results, this work demonstrates the great promise of ZnGa2O4 materials to fabricate high-performance power devices.

Influence of Processing Time in Hydrogen Plasma to Prepare Gallium and Aluminum Codoped Zinc Oxide Films for Low-Emissivity Glass

Low-emissivity glass has high transmission in the visible region and high reflectivity in the infrared region. Gallium and aluminum codoped zinc oxide (GAZO) processed by hydrogen (H2) plasma treatment holds promise for fabricating good low-emissivity glass. The applied processing time is one of the key factors in plasma treatment. The GAZO films were prepared by in-line sputtering at room temperature, and the effect of using different plasma processing times on the structural, electrical and optical properties of the films were surveyed. Experimental results indicate that H2 plasma treatment of GAZO film samples indeed influenced the structure, optical and electrical properties. An appropriate processing time can improve the electrical properties and reduce the emissivity of GAZO films. The optimum processing time is 5 min for plasma treatment of GAZO films. The electrical resistivity and emissivity of plasma-annealed films for 5 min decrease by 59% and 55% compared to those of as-deposited GAZO films. Values of 5.3 × 10−4 Ω-cm in electrical resistivity, 0.13 in emissivity and 94% in average optical transmittance in the visible wavelength region could be obtained for GAZO films after H2 treatment of 5 min in this work for low-emissivity glass applications.

Comparative Study of Atomic Layer Deposited Indium-Based Oxide Transistors with a Fermi Energy Level-Engineered Heterojunction Structure Channel through a Cation Combinatorial Approach.

Amorphous indium-gallium-zinc oxide (a-IGZO) has become a standard channel ingredient of switching/driving transistors in active-matrix organic light-emitting diode (AMOLED) televisions. However, mobile AMOLED displays with a high pixel density (≥500 pixels per inch) and good form factor do not often employ a-IGZO transistors due to their modest mobility (10-20 cm2/(V s)). Hybrid low-temperature polycrystalline silicon and oxide transistor (LTPO) technology is being adapted in high-end mobile AMOLED devices due to its ultralow power consumption and excellent current drivability. The critical issues of LTPO (including a complicated structure and high fabrication costs) require a search for alternative all-oxide thin-film transistors (TFTs) with low-cost processability and simple device architecture. The atomic layer deposition (ALD) method is a promising route for high-performance all-oxide TFTs due to its unique features, such as in situ cation composition tailoring ability, precise nanoscale thickness controllability, and excellent step coverage. Here, we report an in-depth comparative investigation of TFTs with indium-gallium oxide (IGO)/gallium-zinc oxide (GZO) and indium-zinc oxide (IZO)/GZO heterojunction stacks using an ALD method. IGO and IZO layers with different compositions were tested as a confinement layer (CL), whereas the GZO layer was used as a barrier layer (BL). Optimal IGO/GZO and IZO/GZO channels were carefully designed on the basis of their energy band properties, where the formation of a quasi-two-dimensional electron gas (q2DEG) near the CL/BL interface is realized by rational design of the band gaps and work-functions of the IGO, IZO, and GZO thin films. To verify the effect of q2DEG formation, the device performances and stabilities of TFTs with CL/BL oxide heterojunction stacks were examined and compared to those of TFTs with a single CL layer. The optimized device with the In0.75Zn0.25O/Ga0.80Zn0.20O stack showed remarkable electrical performance: μFE of 76.7 ± 0.51 cm2/(V s), VTH of -0.37 ± 0.19 V, SS of 0.13 ± 0.01 V/dec, and ION/OFF of 2.5 × 1010 with low operation voltage range of ≥2 V and excellent stabilities (ΔVTH of +0.35, -0.67, and +0.08 V for PBTS, NBIS, and CCS, respectively). This study suggests the feasibility of using high-performance ALD-derived oxide TFTs (which can compete with the performance of LTPO transistors) for high-end mobile AMOLED displays.

Direct Synthesis of Oxynitride Nanowires through Atmospheric Pressure Chemical Vapor Deposition.

Binary and ternary oxynitride solid alloys were studied extensively in the past decade due to their wide spectrum of applications, as well as their peculiar characteristics when compared to their bulk counterparts. Direct bottom-up synthesis of one-dimensional oxynitrides through solution-based routes cannot be realized because nitridation strategies are limited to high-temperature solid-state ammonolysis. Further, the facile fabrication of oxynitride thin films through vapor phase strategies has remained extremely challenging due to the low vapor pressure of gaseous building blocks at atmospheric pressure. Here, we present a direct and scalable catalytic vapor–liquid–solid epitaxy (VLSE) route for the fabrication of oxynitride solid solution nanowires from their oxide precursors through enhancing the local mass transfer flux of vapor deposition. For the model oxynitride material, we investigated the fabrication of gallium nitride and zinc oxide oxynitride solid solution (GaN:ZnO) thin film. GaN:ZnO nanowires were synthesized directly at atmospheric pressure, unlike the methods reported in the literature, which involved multiple-step processing and/or vacuum operating conditions. Moreover, the dimensions (i.e., diameters and length) of the synthesized nanowires were tailored within a wide range.

Suppression of the Short-Channel Effect in Dehydrogenated Elevated-Metal Metal- Oxide (EMMO) Thin-Film Transistors

Characteristics of amorphous indium- gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) are highly dependent on the hydrogen (H) content within the device architecture, for example in the etch-stop layer (ESL) of the elevated-metal metal-oxide (EMMO) TFTs. The serious apparent “short-channel effect (SCE)” was caused by the H diffusion from source/drain (S/D) to channel. Such SCE deterioration can be suppressed by thermal dehydrogenationat a cost of long annealing time, especially for a transistor architecture with a-IGZO S/D covered with H-rich silicon nitride (SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> :H) and further capped with metallic H-diffusion barrier. The dehydrogenation efficiency is found to be significantly enhanced by fluorinating the a-IGZO. By optimizing the device architecture and/or the fluorination process to enhance the dehydrogenation, the SCE can be efficiently eliminated with well-maintained performance even for 2 μm-long a-IGZO TFTs.

Micromesh-structured flexible polymer white organic light-emitting diodes using single emissive layer of blended polymer and quantum dots

In this study, poly(N-vinylcarbazole) was blended with CdSe/ZnS core-shell quantum dots of various dimensions to be used as a single emissive layer of flexible polymer white organic light-emitting diodes (WOLEDs). A structure of WOLEDs was deposited on polyethylene terephthalate (PET) substrates. A luminance and maximum luminous efficiency of 4070.2 cd/m 2 and 2.84 cd/A were respectively obtained for the WOLEDs prepared using n-type gallium zinc oxide (GZO) and n-type indium gallium zinc oxide (IGZO) films as the electron transport layer and cathode, respectively. Because the current density can be increased by increasing the carrier transport surface area, the 2-μm-periodic SiO 2 micromesh was fabricated on PET substrates to enhance the surface area of a MoO 3 hole transport layer and a GZO electron transport layer. Furthermore, the GZO electron transport layer could provide a moisture barrier function. Compared with WOLEDs without the SiO 2 micromesh, the prepared WOLEDs had an increased current density of 404.5 (compared with 222.8) mA/cm 2 when operating at 11 V. Moreover, their associated luminance and maximum luminous efficiency increased to 7016.1 cd/m 2 and 3.04 cd/A, respectively. The flexible polymer white organic light-emitting diode (WOLED) with single emissive layer constructed by blending PVK with various dimensional CdSe/ZnS core-shell quantum dots were fabricated and investigated. The 2-μm-periodic SiO 2 micromesh was inserted into the bottom side of the IGZO cathode electrode of the WOLEDs to increase the carrier injection surface area and decrease the carrier propagation length. The luminance and the maximum luminous efficiency of the resulting WOLEDs with SiO 2 micromesh were improved from 4070.2 cd/m 2 and 2.84 cd/A to 7016.1 cd/m 2 and 3.04 cd/A, respectively, in comparison with the WOLEDs without SiO 2 micromesh. • The flexible polymer white organic light-emitting diodes (WOLEDs) was fabricated. • Single emissive layer of blended PVK with quantum dots. • Performance of WOLEDs was improved using 2-μm-periodic SiO 2 micromesh. • Luminance of WOLEDs with SiO 2 micromesh was improved from 4070.2 to 7016.1 cd/m 2 . • Luminous efficiency of WOLEDs with SiO 2 micromesh was improved to 3.04 cd/A.

Positive‐negative DC‐DC converter using amorphous‐InGaZnO TFTs

SummaryThis paper presents two DC‐DC converters capable of generating either positive or negative output DC voltage using amorphous‐indium gallium zinc oxide (a‐IGZO) thin‐film transistors (TFTs). While one uses conventional diode‐connected cross‐coupled (design‐1), the other employs a bootstrapped cross‐coupled (design‐2) DC‐DC converter, which overcomes the limitations of design‐1 but requires boosted clock pulses. Therefore, an on‐chip clock booster is proposed to generate all the required signals without any external clock pulses. The performance of the proposed circuits (DC‐DC converters and clock booster) has been demonstrated using in‐house a‐IGZO TFT models in the Cadence environment. The simulation results have shown that design‐1 (design‐2) generates negative or positive output DC voltage of 7.25 V (7.8 V) or 12.7 V (15.2 V), respectively, for a supply voltage of 8 V, using a single DC‐DC converter. Therefore, the output DC voltage of design‐2 is close to the theoretical value, and it ensures robust performance against different load currents when compared with design‐1. Besides, design‐2 has shown a maximum power efficiency of 90%, superior compared with design‐1, where power efficiency is 60.7%. Therefore, this circuit finds potential applications in the next generation flexible displays.