In this study, AlZnON thin-film transistors (TFTs) were fabricated by incorporating aluminum into the ZnON semiconductor and further Schottky contact on the surface of the channel is implemented to enhance the electrical and optical performance of the device. The presence of Al in the thin film improves the reliability of the TFT by stabilizing the nitrogen bond. Further, the optical transmittance improved to 90% from 80% and the bandgap increased to 2.48 eV from 1.89 eV with the doping of Al. The effects of the work function and the widths of the Schottky metal contact on the device characteristics are also investigated. The optimum structure is realized with high work function (5.65 eV) platinum (Pt) metal contact which was positioned at the center of the channel and the width of the Schottky contact was 0.25 times the length of the channel. With the encapsulation of this optimum surface-engineered Schottky contact (SESC) in the device, the field effect mobility increased from 27.3 to 43.9 cm2V-1·s-1, the subthreshold swing reduced from 196 to 113 mV dec-1, threshold voltage changed from -0.13 to 0.12 V and the on-off current ratio improved from 4.13 × 106to 1.03 × 108. The substantial enhancement of transistor performance is achieved through the utilization of a high-work function metal layer, which generates a larger depletion region in the channel, and by precisely controlling the width of the Schottky contact at the channel's center, the depletion region is optimized to suppress off-current while maintaining improved field effect mobility. From the above result, it is evident that the proposed SESC in Al-doped ZnON TFT is a promising candidate for next-generation display application.

Improving the photodetection performance of thin-film transistor (TFT)-based UV photodetectors (UVPDs), using thick channel layers to promote photocurrent ( I ph ) or using thin channel layers to suppress dark current ( I dark ) is typically a trade-off. In this work, UVPDs based on oxygen-doped Si-Zn-Sn-O (SZTO) TFT with a stack of Pt/NiO capping layers (CLs) to release the trade-off between I dark and I ph are demonstrated. The Pt CL creates a wide depletion region in the channel layer to allow the use of thick channels, but still maintains low I dark , while the NiO CL forms a pn heterojunction to provide additional photogenerated carriers and enhance I ph under UV irradiation. Experimental results show that the proposed 95 nm-thick oxygen-doped SZTO TFT with a stack of Pt/NiO dual CLs exhibits an excellent photoresponsivity of 2026 A W −1 and photosensitivity of 9.3 × 10 7 A A −1 , which are about 76× and 82.5× higher than a conventional 45 nm-thick SZTO TFT under 275 nm UV irradiation.

Ultraviolet photodetectors (UVPDs) based on Si-Zn-SnO (SZTO) thin-film transistors (TFTs) with a stacked dual-channel layer (DCL) structure with different carrier concentration and NiO capping layer (CL) to alleviate the trade-off between dark current ( I dark ) and photocurrent ( I ph ) are reported. Experimental results show that under 275 nm irradiation, the proposed SZTO TFT UVPD with a 30 nm thick upper layer stacked on a 50 nm thick channel layer and a patterned NiO CL exhibit excellent photoresponsivity and photosensitivity up to 1672 A W −1 and 1.03 × 10 7 A A −1 , which is about 272 and 137 times higher than conventional 30 nm thick single-channel layer SZTO TFT. These improvements are due to the use of a DCL which forms a high-low junction to reduce the effective channel thickness and increasing the space for UV illumination and the use of NiO CL lowers the I dark and causes a considerable negative threshold voltage shift under UV irradiation to significantly boost the I ph .

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.

In this work, staggered bottom-gate structure amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) with high-k ZrO2 gate dielectric were fabricated using low-cost atmospheric pressure-plasma enhanced chemical vapor deposition (AP-PECVD) with in situ hydrogenation to modulate the carrier concentration and improve interface quality. Subsequently, a neutral oxygen beam irradiation (NOBI) technique is applied, demonstrating that a suitable NOBI treatment could successfully enhance electrical characteristics by reducing native defect states and minimize the trap density in the back channel. A reverse retrograde channel (RRGC) with ultra-high/low carrier concentration is also formed to prevent undesired off-state leakage current and achieve a very low subthreshold swing. The resulting a-IGZO TFTs exhibit excellent electrical characteristics, including a low subthreshold swing of 72 mV dec(-1) and high field-effect mobility of 35 cm(2) V-1 s(-1), due to conduction path passivation and stronger carrier confinement in the RRGC. The UV-vis spectroscopy shows optical transmittance above 90% in the visible range of the electromagnetic spectrum. The study confirms the H-2 plasma with NOBI-treated a-IGZO/ZrO2 TFT is a promising candidate for transparent electronic device applications.

Ultraviolet photodetectors (UVPDs) based on diode-connected In-Ga-ZnO (IGZO) thin-film transistors (TFTs), called field-effect diodes (FEDs), are presented. A patterned NiO capping layer (CL) deposited on the top surface of the IGZO channel forming a heterojunction (HJ) was employed to further improve UV detection performance. Experimental results show that FED-based UVPDs have advantages over traditional TFT-based UVPDs, achieving a minimum dark current without additional gate bias and a wider bias range for detection measurements. UVPDs based on the 30-nm-thick IGZO FED with NiO CL show a photoresponsivity and photosensitivity of up to 1376 A/W and $9.10\times10$ 7 A/A at 275 nm under ${V} _{D}$ = −1.5 V, which is about $25\times $ and $1480\times $ higher than the case without NiO CL. These improvements are due to the fact that the NiO CL/IGZO HJ reduces the effective channel thickness to suppress dark current and provide additional optically generated electrons in the channel and an additional negative threshold voltage shift to enhance the photocurrent.

Sensing electrodes (SEs) fabricated by a multiple surface roughening scheme based on KOH-etched Si substrates with spraying deposited multi-walled carbon nanotubes (MWCNTs) and hydrothermally grown (HTG) NiO nanosheets (NSs) to improve pH sensing performance are demonstrated. A surface area (SA) gain of around 2.31 is obtained from the etched Si substrate, which results in an enhancement in the pH sensitivity of MWCNTs SEs from 52.15 to 54.95 mV pH −1 based on Si substrates without and with KOH etching. Effects of the thermal annealing temperatures and spraying times of the MWCNTs and HTG times of NiO NSs of the proposed NiO NSs/MWCNTs/pyramid-Si SEs on pH sensitivity, hysteresis, and reliability are studied. A near-Nernstian response of 57.56 mV pH −1 is obtained, which could be attributed to the proposed method maximize SA and the number of ion adsorption sites for advancing pH sensing performance.

A physical assessment of the lateral gate-all-around (GAA) nanosheet transistor (NSFET) at the G40M16 node (gate length = 12 nm projected for 2028) of the newly defined beyond-Moore International Roadmap for Devices and Systems [~5 nm node of the predecessor International Technology Roadmap for Semiconductors (ITRS)], supported by 3-D numerical device simulations and based on a proposed per-footprint scheme, is presented. The traditional evaluation scheme to gauge the performance of the transistor “per effective channel width” is shown to be improper due to pervasive bulk inversion. Bulk inversion, along the width of the nanosheet and at its ends, obfuscates the dependence of current on sheet/channel width and undermines the presumed added benefit of short-channel effect (SCE) control in the GAA device. The NSFET provides a flexible sheet width, as opposed to that of the FinFET with discrete fins, but the allowed range of sheet width is limited due to significant parasitic capacitance at a relatively narrow width and degraded SCE control and increased resistance for desired wide width. Furthermore, the nanosheet (NS) device density is undermined at a narrow width, especially for decreasing pitch. The FinFET is shown to be a favorable alternative to the NSFET even at the G40M16 node.

A dual surface roughening scheme using a KOH-etched Si (100) substrate for the hydrothermal growth (HTG) of NiO nanosheets (NSs) to improve pH sensing performance is demonstrated. The effects of the KOH etching conditions and the HTG time for the synthesis of NSs on the pH sensing response are discussed. The NiO NS sensing electrode (SE) based on a KOH-etched Si substrate showed a near-perfect linearity of 0,999 and a near-Nernstian response of 56.5 mV pH(-1). As compared with an NS-type SE based on planar Si (53.64 mV pH(-1)) and an SE based on sputtering NiO on a KOH-etched Si substrate (52.87 mV pH(-1)), an enhancement in pH sensitivity of 5.33% and 6.87% was achieved, respectively. It is attributed to the fact that the dual surface roughening scheme greatly increased the sensing area and the number of surface sites for ion adsorption. (C) 2020 The Japan Society of Applied Physics

A thin-film transistor (TFT) with a Ti-IGZO channel layer and Hf1-xAlxO gate dielectric is proposed to improve the performance and reliability of the device. The experimental results show that in three types of TFTs based on HfO2/IGZO, Hf1-xAlxO/IGZO and Hf1-xAlxO/Ti-IGZO gate dielectric/channel structures, the Hf0.88Al0.12O/Ti (2.0%)-IGZO TFT exhibits the best device performance with the subthreshold swing of 86 mV dec(-1), field-effect mobility of 28.63 cm(2).V-1.s(-1) and on/off current ratio of 3.26 x 10(8). In particular, it shows a hysteresis voltage as low as 0.02 V and a threshold voltage shift after 1000 s positive/negative gate bias stress/white light illumination of 0.134 V/-0.089 V/-0.195 V, compared with 0.45 V and 0.612 V/-0.507 V/-0.657 V of the HfO2/IGZO TFT. These improvements are due to the incorporation of Ti into the IGZO channel, which reduces defect density, while adding Al to HfO2 improves surface roughness to inhibit surface scattering and charge capture during stress testing. (C) 2020 The Japan Society of Applied Physics

2020 International Conference on Solid State Devices and Materials ,The Use of a Multiple Roughening Scheme to Enhance Sensing Performance of pH Sensors with NiO Nanosheets/MWCNTs on KOH-etched Si Substrate

Introduction: Recently, the use of high surface-to-volume ratio sensing materials, such as TiO 2 , ZnO, and NiO nanostructures, used for pH sensing were demonstrated [ 1 – 4 ]. High response over 44.5 mV/pH was obtained, which was explained as being attributed to increase ion adsorption sites of sensing electrodes (SEs). In this work, pH SEs with improved sensing performance based on hydrothermal growth (HTG) of NiO NSs on Hierarchically roughened Si substrates, which could significantly increase the ion adsorption sites, are proposed and demonstrated. A dual roughening scheme to form pyramidal cones and Si nanowires (Si NWs) consecutively is employed. For comparison, pH sensing performance of SEs with a different combination of the Si NWs, KOH-etched Si substrates, and HTG NiO NSs are also investigated and the benefit of the nanostructures is analyzed. Possible mechanism governing the enhancement in pH sensing response is also proposed and discussed.

2020 International Conference on Solid State Devices and Materials ,Enhanced Electrical Performance and Reliability of Ti-SZTO Thin-Film Transistors with Hf1-xSixO2 Gate Dielectrics Using Co-sputtering Technique

2020 International Conference on Solid State Devices and Materials ,The Use of a Patterned NiO Capping Layer to Improve Photoresponsivity of Ultraviolet Photodetectors Based on IGZO Field Effect Diodes

2019 International Conference on Solid State Devices and Materials ,Enhanced Electrical Performance and Reliability of Ti-IGZO Thin-Film Transistors with HfxAl1-xO Gate Dielectrics

This paper proposes vertically stacked gate-all-around MOSFET structure with optimized inner spacers to provide superior gate controllability and reduce additional parasitic capacitance simultaneously. To achieve better performance, we evaluate different inner spacer lengths while tuning source/drain doping profile to keep off-state leakage current unchanged. Considering the fabrication uniformity, the key of the conceptual process flow is to etch inner spacers selectively from top to bottom channel. The proposed approach can be applied to low power and ultra-low power design for SoC application without additional mask cost.

A comparative study of the performance of lateral- and vertical-structured UV photodetectors (PDs) based on a hydrothermally grown (HTG) n-ZnOtsputtered p-CuO heterojunction (HJ) is presented. After substrate transfer (ST) conducted using a sonicating bath process, the vertical-structured UV PD showed a fast response and a 310-fold improvement in light responsivity compared with that of the lateral-structured UV PD under UV illumination (365 nm at 3 mW cm(-2)) at a reverse bias of -1 V. This improvement is attributed to the much shorter conduction path and lake of a seed layer for the vertical structure. With further surface chemical etching of the HTG n-ZnO layer after ST, a pyramid-like surface texture formed and a significantly enhanced UV light response (as high as 943-fold higher) was obtained. The increase in photo-responsivity is due to the removal of the high defect density initial ZnO growth layer and reduced light reflection. (C) 2019 The Japan Society of Applied Physics