Indium Gallium Zinc Oxide Channel Research Articles

An Optimized Device Structure with Improved Erase Operation within the Indium Gallium Zinc Oxide Channel in Three-Dimensional NAND Flash Applications

In this paper, we propose an optimized device structure to address issues in 3D NAND flash memory devices, which encounter difficulties when using the hole erase method due to the unfavorable hole characteristics of indium gallium zinc oxide (IGZO). The proposed structure mitigated the erase operation problem caused by the low hole mobility of IGZO by introducing a filler inside the IGZO channel. It facilitated the injection of holes into the IGZO channel through the filler, while the existing P-type doped polysilicon filler material was replaced by a P-type oxide semiconductor. In contrast to polysilicon (band gap: 1.1 eV), this P-type oxide semiconductor has a band gap similar to that of the IGZO channel (2.5 to 3.0 eV). Consequently, it was confirmed through device simulation that there was no barrier due to the difference in band gaps, enabling the seamless supply of holes to the IGZO channel. Based on these results, we conducted a simulation to determine the optimal parameters for the P-type oxide semiconductor to be used as a filler, demonstrating improved erase operation when the P-type carrier density was 1019 cm−3 or higher and the band gap was 3.0 eV or higher.

Light-Stimulated IGZO Transistors with Tunable Synaptic Plasticity Based on Casein Electrolyte Electric Double Layer for Neuromorphic Systems.

In this study, optoelectronic synaptic transistors based on indium-gallium-zinc oxide (IGZO) with a casein electrolyte-based electric double layer (EDL) were examined. The casein electrolyte played a crucial role in modulating synaptic plasticity through an internal proton-induced EDL effect. Thus, important synaptic behaviors, such as excitatory post-synaptic current, paired-pulse facilitation, and spike rate-dependent and spike number-dependent plasticity, were successfully implemented by utilizing the persistent photoconductivity effect of the IGZO channel stimulated by light. The synergy between the light stimulation and the EDL effect allowed the effective modulation of synaptic plasticity, enabling the control of memory levels, including the conversion of short-term memory to long-term memory. Furthermore, a Modified National Institute of Standards and Technology digit recognition simulation was performed using a three-layer artificial neural network model, achieving a high recognition rate of 90.5%. These results demonstrated a high application potential of the proposed optoelectronic synaptic transistors in neuromorphic visual systems.

A Thin-Film Pinned-Photodiode Imager Pixel with Fully Monolithic Fabrication and beyond 1Me- Full Well Capacity.

Thin-film photodiodes (TFPD) monolithically integrated on the Si Read-Out Integrated Circuitry (ROIC) are promising imaging platforms when beyond-silicon optoelectronic properties are required. Although TFPD device performance has improved significantly, the pixel development has been limited in terms of noise characteristics compared to the Si-based image sensors. Here, a thin-film-based pinned photodiode (TF-PPD) structure is presented, showing reduced kTC noise and dark current, accompanied with a high conversion gain (CG). Indium-gallium-zinc oxide (IGZO) thin-film transistors and quantum dot photodiodes are integrated sequentially on the Si ROIC in a fully monolithic scheme with the introduction of photogate (PG) to achieve PPD operation. This PG brings not only a low noise performance, but also a high full well capacity (FWC) coming from the large capacitance of its metal-oxide-semiconductor (MOS). Hence, the FWC of the pixel is boosted up to 1.37 Me- with a 5 μm pixel pitch, which is 8.3 times larger than the FWC that the TFPD junction capacitor can store. This large FWC, along with the inherent low noise characteristics of the TF-PPD, leads to the three-digit dynamic range (DR) of 100.2 dB. Unlike a Si-based PG pixel, dark current contribution from the depleted semiconductor interfaces is limited, thanks to the wide energy band gap of the IGZO channel material used in this work. We expect that this novel 4 T pixel architecture can accelerate the deployment of monolithic TFPD imaging technology, as it has worked for CMOS Image sensors (CIS).

Analog Synaptic Devices Based on IGZO Thin‐Film Transistors with a Metal–Ferroelectric–Metal–Insulator–Semiconductor Structure for High‐Performance Neuromorphic Systems

A ferroelectric thin‐film transistor (FeTFT)‐based synaptic device with an indium–gallium–zinc oxide (IGZO) channel and a metal–ferroelectric–metal–insulator–semiconductor (MFMIS) structure is reported. The fabricated FeTFT exhibits a highly linear conductance response (|α| = 0.21) with a large dynamic range (Gmax/Gmin ≈ 53.2), although identical program pulses are applied to the device. In addition, because the inner metal layer of the FeTFTs has an MFMIS structure, the electric field is uniformly applied to the entire IGZO channel, which reduces the cycle‐to‐cycle variation (σ = 0.47%) in the conductance responses. In the system simulation with the measured synaptic characteristics, the high classification accuracy of ≈97.0% is achieved in the MNIST image set, verifying the feasibility of FeTFT‐based neuromorphic systems.

Enhancing photodetection performance of UV photodetectors with stacked Pt/NiO dual capping layers on IGZO thin-film transistors

This paper proposes a solution to mitigate the trade-off between dark and photocurrents in the indium gallium zinc oxide (IGZO) thin-film transistor (TFT) applications, such as ultraviolet photodetectors, by using a stacked Pt/NiO dual capping layer (CL). The Pt CL forms a Schottky contact with the IGZO channel, which maximizes the depletion width on the channel layer and allows the use of a thicker channel to suppress both dark current and channel resistance. On the other hand, the NiO CL forms a pn heterojunction with the IGZO channel, which provides additional space for generating electron–hole pairs and is forward biased by the photovoltaic voltage under UV irradiation, resulting in a further negative shift in the threshold voltage and a significant increase in photocurrent. Experimental results show that the proposed CL scheme exhibits excellent photoresponsivity, photosensitivity, and specific detectivity in a 40 nm-thick IGZO TFT, with the values of 1888 A/W, 3.37 × 108 A/A, and 3.99 × 1016 Jones, respectively, which are about 55%, 83%, and 68% higher than a traditional 30 nm-thick IGZO TFT using only NiO CL under 275 nm UV irradiation.

Write-Once-Read-Many-Times Memory Characteristics with a Large Memory Window Operating at a Low Voltage by Li-Ion Incorporation from the LiCoOx Ion-Supplying Layer into the InGaZnO Channel of a Thin-Film Transistor

Write-once-read-many-times (WORM) memory characteristics with a large memory window are demonstrated in a thin-film transistor (TFT) composed of an indium-gallium-zinc oxide (IGZO) channel and a lithium-cobalt oxide (LiCoOx) ion-supplying layer in the gate oxide. While the device with a thicker (5 nm) tunneling oxide showing a threshold voltage shift (ΔVT) of about 5 V by electron charging upon positive gate voltage (VGS) sweep to +25 V, the device with a 2 nm-thick tunneling oxide exhibits a large memory window with ΔVT > 20 V by Li-ion migration from LiCoOx to IGZO channel, which can be controlled as multilevel states with respect to the VGS amplitude. Incorporation of Li ions into the IGZO channel acting as p-type dopants reduces carrier concentration in the channel and consequently increases VT. The increased VT and the consequently reduced drain current are not instantly restored back by applying negative VGS, featuring WORM memory characteristics. Although the device undergoes partial retention loss, the retention remains up to about 90% after 100 min of retention time. These results verify WORM memory operations in the IGZO TFTs through gate voltage-driven Li-ion incorporation into the IGZO channel to modify its conductive states instead of using a typical electrical charging route.

IGZO thin-film transistors with tunneling contacts: towards power efficient display

We report the fabrication and characterization of indium gallium zinc oxide (IGZO) tunneling thin-film transistors. Both the IGZO channel and an Al2O3 tunneling barrier layer were deposited using the radio-frequency magnetron sputtering method. Compared with a conventional device, our device exhibited rapid saturation at a much smaller drain bias. Interestingly, we observed two different current saturation mechanisms within a single device, which can be explained as competition between the depletion envelope near the source electrode and channel depletion near the drain electrode. This work represents an industry-friendly method for implementing the tunnel-contact approach in the display industry.

Synaptic Transistor Based on In‐Ga‐Zn‐O Channel and Trap Layers with Highly Linear Conductance Modulation for Neuromorphic Computing

AbstractBrain‐inspired neuromorphic computing has drawn significant attraction as a promising technology beyond von Neumann architecture by using the parallel structure of synapses and neurons. Various artificial synapse configurations and materials have been proposed to emulate synaptic behaviors for human brain functions such as memorizing, learning, and visual processing. Especially, the memory type indium‐gallium‐zinc‐oxide (IGZO) synaptic transistor adopting a charge trapping layer (CTL) has the advantages of high stability and a low leakage current of the IGZO channel. However, the CTL material should be carefully selected and optimized to overcome the low de‐trapping efficiency, resulting from difficulty in inducing holes in the IGZO channel. In this paper, IGZO is adopted as a CTL and found out that making it degenerated is crucial to improving de‐trapping efficiency. The degenerate CTL, where electrons remain as free electrons, induces Fowler‐Nordheim tunneling by increasing the electric field across the tunneling layer. As a result, the synaptic transistor represents a high linearity of potentiation (αp: −0.03) and depression (αd: −0.47) with 64 conductance levels, which enables the spiking neural network simulation to achieve high accuracy of 98.08%. These experimental results indicate that the synapse transistor can be one of the promising candidates for neuromorphic applications.

True Nonvolatile High-Speed DRAM Cells Using Tailored Ultrathin IGZO.

Severe power consumption in the continuous scaling of Silicon-based dynamic random access memory (DRAM) technology quests for a transistor technology with a much lower off-state leakage current. Wide bandgap amorphous oxide semiconductors, especially indium-gallium-zinc-oxide (IGZO)exhibit many orders of magnitude lower off-state leakage. However, they are typically heavily n-doped and require negative gate voltage to turn off, which prevents them from true nonvolatile operation. The efforts on doping density reduction typically result in mobility degradation and high Schottky barriers at contacts, causing severe degradation of on-current and operation speed of the DRAM cells. Here, high-speed true nonvolatile DRAM cells are successfully demonstrated by deep suppression of doping density in the IGZO channel using in situ oxygen ion beam treatment and ohmic contact engineering by inserting a thin In-rich indium-tin-oxide (ITO) at contact regions. A record high on-current of 40µA µm-1 at a large positive threshold voltage of 1.78V enables the first true nonvolatile DRAM with the fastest write speed of 10ns and data retention up to 25 h under power interruption, five orders of magnitude higher than the previously projected values.

Ferroelectric Content-Addressable Memory Cells with IGZO Channel: Impact of Retention Degradation on the Multibit Operation.

Indium gallium zinc oxide (IGZO)-based ferroelectric thin-film transistors (FeTFTs) are being vigorously investigated for being deployed in computing-in-memory (CIM) applications. Content-addressable memories (CAMs) are the quintessential example of CIM, which conduct a parallel search over a queue or stack to obtain the matched entries for a given input data. CAM cells offer the ability for massively parallel searches in a single clock cycle throughout an entire CAM array for the input query, thereby enabling pattern matching and searching functionality. Therefore, CAM cells are used extensively for pattern matching or search operations in data-centric computing. This paper investigates the impact of retention degradation on IGZO-based FeTFT on the multibit operation in content CAM cell applications. We propose a scalable multibit 1FeTFT-1T-based CAM cell composed of only one FeTFT and one transistor, thus significantly improving the density and energy efficiency compared with conventional complementary metal-oxide-semiconductor (CMOS)-based CAM. We successfully demonstrate the operations of our proposed CAM with storage and search by exploiting the multilevel states of the experimentally calibrated IGZO-based FeTFT devices. We also investigate the impact of retention degradation on the search operation. Our proposed IGZO-based 3-bit and 2-bit CAM cell shows 104 s and 106 s retention, respectively. The single-bit CAM cell shows lifelong (10 years) retention.

Device modeling of two-steps oxygen anneal-based submicron InGaZnO back-end-of-line field-effect transistor enabling short-channel effects suppression

Amorphous oxide semiconductor (AOS) field-effect transistors (FETs) have been integrated with complementary metal-oxide-semiconductor (CMOS) circuitry in the back end of line (BEOL) CMOS process; they are promising devices creating new and various functionalities. Therefore, it is urgent to understand the physics determining their scalability and establish a physics-based model for a robust device design of AOS BEOL FETs. However, the advantage emphasized to date has been mainly an ultralow leakage current of these devices. A device modeling that comprehensively optimizes the threshold voltage (VT), the short-channel effect (SCE), the subthreshold swing (SS), and the field-effect mobility (µFE) of short-channel AOS FETs has been rarely reported. In this study, the device modeling of two-steps oxygen anneal-based submicron indium-gallium-zinc-oxide (IGZO) BEOL FET enabling short-channel effects suppression is proposed and experimentally demonstrated. Both the process parameters determining the SCE and the device physics related to the SCE are elucidated through our modeling and a technology computer-aided design (TCAD) simulation. In addition, the procedure of extracting the model parameters is concretely supplied. Noticeably, the proposed device model and simulation framework reproduce all of the measured current–voltage (I–V), VT roll-off, and drain-induced barrier lowering (DIBL) characteristics according to the changes in the oxygen (O) partial pressure during the deposition of IGZO film, device structure, and channel length. Moreover, the results of an analysis based on the proposed model and the extracted parameters indicate that the SCE of submicron AOS FETs is effectively suppressed when the locally high oxygen-concentration region is used. Applying the two-step oxygen annealing to the double-gate (DG) FET can form this region, the beneficial effect of which is also proven through experimental results; the immunity to SCE is improved as the O-content controlled according to the partial O pressure during oxygen annealing increases. Furthermore, it is found that the essential factors in the device optimization are the subgap density of states (DOS), the oxygen content-dependent diffusion length of either the oxygen vacancy (VO) or O, and the separation between the top-gate edge and the source-drain contact hole. Our modeling and simulation results make it feasible to comprehensively optimize the device characteristic parameters, such as VT, SCE, SS, and µFE, of the submicron AOS BEOL FETs by independently controlling the lateral profile of the concentrations of VO and O in two-step oxygen anneal process.

Ultra-large dynamic range synaptic indium gallium zinc oxide transistors

Three-terminal neuromorphic transistors have garnered considerable attention owing to their superior learning and recognition capabilities in neural computing. For efficient and rapid computing of parallel arithmetic and unstructured large-sized data, a high-synaptic channel conductance (G) (i.e., synaptic weight) and large dynamic range (DR) (i.e., weight update) are necessary. In this study, we successfully fabricated high-performance and all-solution-processed synaptic transistors by employing a thiol–ene photoclick chemistry-based, cross-linked vinyl addition polynorbornene copolymer dielectric layer, poly(norbornene-co-5-vinyl-2-norbornene) (P(NB/VNB)) and sol-gel-derived indium gallium zinc oxide (IGZO) semiconducting channel layer. The molecular behaviors of free hydroxyl group in the dielectric layer formed via ultraviolet photo-induced thiol–ene click reactions of the polar cross-linker pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) allows slow dipole polarization effects on the IGZO channel layer. An exhaustive and systemic investigation of the surface physicochemical and electrical properties confirmed that the mutual interface coupling between the cross-linked P(NB/VNB) dielectric and IGZO semiconductor exhibited remarkable synaptic functionality with a high G (∼540 μS), large DR (∼6213), and long-term operational stability following excitation with 104 successive pulses that resulted in neural recognition accuracy of 87.11% based on the use of MNIST database set which is close to ideal value of 88%. This high-performance synaptic transistor based on all-solution-derived functional organic–inorganic hybrid stack layers can serve as a basis for the successful implementation of novel neuromorphic computing systems that satisfy the requirements for strong neuronal signal transmission and distinguishable multi-level data states.

(Digital Presentation) High Performance Back-Channel-Etch Igzo TFT with Self-Passivate HfO2 By Backside Exposure Technology

Recently, amorphous oxide semiconductor (AOS)-based TFTs have drawn much attention for the backplane technologies of the ultra-high resolution TFT-LCDs and AMOLEDs [1-2]. To overcome the degradation of electrical characteristics caused by the ambient, a passivation layer capsulation is proposed to solve the problem. In this work, a capping layer of HfO2 film is studied acting as both a passivation layer and an etch stop layer for TFT device structure with the back channel etching (BCE) process. The BCE type of indium-gallium-zinc-oxide (IGZO) TFT is successfully demonstrated with a self-aligned backside exposure method for the photo-mask reduction, which not only decreases the complexity of the device fabrication but also lowers the manufacturing cost [3-4].ExperimentAmorphous IGZO TFTs with a bottom gate staggered structure were fabricated in this work. A layer of metallic Mo thin film was first deposited on a glass substrate by DC sputtering and patterned as the gate electrode. It was followed by the deposition of HfO2 film as gate insulator and a-IGZO as channel layer by RF sputtering. Besides, a HfO2 capping layer was deposited on top of IGZO channel layer as the passivation and etch stop layer (ESL). The self-aligned backside exposure process was then implemented to pattern the IGZO channel layer and ESL simultaneously. And Mo source/drain (S/D) electrodes were formed to finish the BCE a-IGZO TFT manufacture. The IGZO TFT was also fabricated with a lift-off S/D process. Firstly, the exposure of the S/D area patterns was executed by removing the photoresist covered on the top of the S/D in the development process. Then, a layer of Mo film was deposited by DC sputtering, and followed by performing the lift-off process in acetone for the photoresist stripping. Thus, the open hole on S/D pattern areas will be filled with Mo and form S/D electrodes. The manufacture of lift-off S/D IGZO TFT was completed, and it will be compared with the characteristics of BCE a-IGZO TFT.Result and DiscussionThe experimental results have shown that the HfO2 capping layer can keep IGZO channel from exposing to oxygen and hydrogen in the atmosphere. Also, HfO2 capping layer could be acting as etching stop layer to protect IGZO channel from the damage during BCE process. As compared with a lift-off S/D process without BCE damage, the nearly non-degraded BCE a-IGZO TFT in this work demonstrates the compatible performance such as threshold voltage of 0.03 V, an approximately ideal sub-threshold swing of 65.8 mV/dec., field-effect mobility of 9.91 cm2/V·s, on/off current ratio of 6×107 (at VD=0.1 V), and extremely low electrical hysteresis loop of ~ 0 mV was obtained successfully. Furthermore, the self-aligned process with backside exposure could lower the cost for device fabrication by decreasing the number of photomasks, and the BCE process have the ability for channel size scaling. With the excellent characteristics mentioned above, the BCE a-IGZO TFT is highly applicable to the emerging high-resolution display technologies.Reference[1] T. Kamiya, K. Nomura , and H. Hosono, Science and Technology of Advanced Materials, vol. 11, no. 4, pp. 044305, 2010.[2] P. Y. Kuo, C. M. Chang, I. H. Liu, and P. T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019.[3] Y. Kuo, Journal of The Electrochemical Society, vol. 138, no. 2, pp. 637, 1991.[4] N. Münzenrieder, P. Voser, L. Petti, C. Zysset, L. Büthe, C. Vogt, G. A. Salvatore, and G. Tröster, IEEE Electron Device Letters, vol. 35, no. 1, pp. 69, 2014. Figure 1

IGZO nanofiber photoelectric neuromorphic transistors with indium ratio tuned synaptic plasticity

Synaptic plasticity divided into long-term and short-term categories is regarded as the origin of memory and learning, which also inspires the construction of neuromorphic systems. However, it is difficult to mimic the two behaviors monolithically, which is due to the lack of time-tailoring approaches for a certain synaptic device. In this Letter, indium-gallium-zinc-oxide (IGZO) nanofiber-based photoelectric transistors are proposed for realizing tunable photoelectric synaptic plasticity by the indium composition ratio. Notably, short-term plasticity to long-term plasticity transition can be realized by increasing the ratio of indium in the IGZO channel layer. The spatiotemporal dynamic logic and low energy consumption (<100 fJ/spike) are obtained in devices with low indium ratio. Moreover, the symmetric spike-timing-dependent plasticity is achieved by exploiting customized light and electric pulse schemes. Photoelectric long-term plasticity, multi-level characteristics, and high recognition accuracy (93.5%) are emulated in devices with high indium ratio. Our results indicate that such a composition ratio modulated method could enrich the applications of IGZO nanofiber neuromorphic transistors toward the photoelectric neuromorphic systems.

Solid‐State Optoelectronic Synapse Transistor Using a LaF3 Gate Dielectric

As a new generation of core components for neuromorphic computing, optoelectronic synaptic devices have the advantages of high bandwidth and less energy consumption. They can combine the functions of visual sensing, signal processing, and memory in one device. Herein, an all‐solid‐state optoelectronic synaptic transistor using indium gallium zinc oxide (IGZO) as the channel and lanthanum fluoride (LaF3) as the gate dielectric is designed and fabricated. Its synaptic plasticity induced by electric and optical stimuli is investigated. LaF3 is a solid superionic conductor with plenty of mobile fluoride ions, which can be used to achieve a high on/off ratio of more than 105 and a low subthreshold swing less than 150 mV dec−1 in this novel synaptic transistor. Due to the ion‐trapping effect at the interface, synaptic plasticity can be achieved upon electrical stimulation. Synaptic plasticity by light pulse stimuli can also be accomplished with the assistance of the persistent photoconductivity effect in IGZO channel. Furthermore, it is found that the synaptic plasticity induced by light stimuli can be modulated by gate voltage. These results provide a new way to control synaptic function and extend the function of optoelectronic synaptic devices.

IGZO synaptic thin-film transistors with embedded AlO x charge-trapping layers

We report the fabrication and characterization of indium gallium zinc oxide (IGZO)-based synaptic thin-film transistors. Radio-frequency magnetron-sputtered AlO x thin films are embedded in the IGZO channel as charge-trapping layers to provide synaptic behavior. The voltage pulse introduced at the gate electrodes traps or de-traps charges in the embedded AlO x layer thus modulates the channel current, which in turn leads to the ability to mimic biological synaptic behaviors such as excitonic postsynaptic current, paired-pulse facilitation, and potentiation and depression. Simulation results suggest that the device can perform properly as a synaptic unit in an artificial neural network.

Realization of Enhanced Long‐Term Visual Memory for Indium–Gallium–Zinc Oxide‐Based Optical Synaptic Transistor

AbstractAmorphous indium–gallium–zinc oxide (IGZO)‐based optical synaptic transistor using visible light as the signal that shows a clear difference between long‐term memory (LTM) and short‐term memory (STM) is introduced in this study. However, since oxide semiconductors, including IGZO, do not sense visible light due to their high band gap energy of around 3.0 eV, defects are generated intentionally within IGZO channel layer to enable sensitivity to the visible light by inserting two layers of mesh‐structured titanium dioxide (m‐TiO2) inside the channel layer. Additionally, a layer of thin film‐structured hafnium dioxide (HfO2) is inserted inside the channel to increase the persistent photoconductivity (PPC) effect. This increased PPC effect causes the device to maintain the current long after the light signal is removed. Therefore, the average difference between LTM and STM is achieved ≈110 times, showing a clear difference between LTM and STM. Additionally, 721% of maximum paired‐pulse facilitation (PPF) is achieved. Thus, the device introduced in this study is believed to lead the coming technology such as interactive appliances including displays and robots.

Influence of UV/Ozone Treatment on Threshold Voltage Modulation in Sol–Gel IGZO Thin‐Film Transistors

AbstractSol–gel indium–gallium–zinc oxide (IGZO) semiconductors are developed as active components of thin‐film transistors (TFTs) because of their high electron mobility, cost‐effective large‐area fabrication, and applicability for flexible substrates. Controlling oxygen vacancies (Vo) in the IGZO semiconductor channel is always problematic for reliable and long‐term operation. Surplus interfacial charges inside the IGZO channel cause negative shifts in threshold voltages (Vth), resulting in depletion‐mode operation and involuntary high current output. The room temperature and rapid (<3 min) modulation of Vth using a novel ultraviolet ozone (UVO) treatment of IGZO layer (In:Ga:Zn = 7:1:2) are reported. Physicochemical and electrical analysis reveals that UVO treatment enables the reduction of Vo and increases MO bonding with invariant contact resistance, resulting in the normalization of Vth close to 0 V and high operational durability under long‐term bias stress. As a proof of concept, this study demonstrates the depletion‐load n‐type inverters comprising depletion and enhancement modes (without & with UVO) on the same substrate that allow high gain (≈10) with a moderate noise margin. This UVO treatment of the active layer is advantageous for the effective modulation of Vth with stable operation under long‐term bias stress and is superior to logic inverters based on single‐mode sol–gel oxide transistors.

Memory Characteristics of Thin Film Transistor with Catalytic Metal Layer Induced Crystallized Indium-Gallium-Zinc-Oxide (IGZO) Channel

The memory characteristics of a flash memory device using c-axis aligned crystal indium gallium zinc oxide (CAAC-IGZO) thin film as a channel material were demonstrated. The CAAC-IGZO thin films can replace the current poly-silicon channel, which has reduced mobility because of grain-induced degradation. The CAAC-IGZO thin films were achieved using a tantalum catalyst layer with annealing. A thin film transistor (TFT) with SiO2/Si3N4/Al2O3 and CAAC-IGZO thin films, where Al2O3 was used for the tunneling layer, was evaluated for a flash memory application and compared with a device using an amorphous IGZO (a-IGZO) channel. A source and drain using indium-tin oxide and aluminum were also evaluated for TFT flash memory devices with crystallized and amorphous channel materials. Compared with the a-IGZO device, higher on-current (Ion), improved field effect carrier mobility (μFE), a lower body trap (Nss), a wider memory window (ΔVth), and better retention and endurance characteristics were attained using the CAAC-IGZO device.

Enhanced Ultraviolet Photoresponse Characteristics of Indium Gallium Zinc Oxide Photo-Thin-Film Transistors Enabled by Surface Functionalization of Biomaterials for Real-Time Ultraviolet Monitoring.

Indium gallium zinc oxide (IGZO) is one of the most promising materials for diverse optoelectronic applications based on thin-film transistors (TFTs) including ultraviolet (UV) photodetectors. In particular, the monitoring of UV-A (320-400 nm) exposure is very useful for healthcare applications because it can be used to prevent various human skin and eye-related diseases. However, the relatively weak optical absorption in the UV-A range and the persistent photoconductivity (PPC) arising from the oxygen vacancy-related states of IGZO thin films limit efficient UV monitoring. In this paper, we report the enhancement of the UV photoresponse characteristics of IGZO photo-TFTs by the surface functionalization of biomolecules on an IGZO channel. The biomaterial/IGZO interface plays a crucial role in enhancing UV-A absorption and suppressing PPC under negative gate bias, resulting in not only increased photoresponsivity and specific detectivity but also a fast and repeatable UV photoresponse. In addition, turning off the device without external bias completely eliminates PPC due to the internal electric field induced by the surface functionalization of biomaterials. Such a volatile feature of PPC enables the fast and repeatable UV photoresponse. These results suggest the potential of IGZO photo-TFTs combined with biomaterials for real-time UV monitoring.