Post-deposition Annealing Process Research Articles

Improved electrical performance for SiO2/β-Ga2O3 (001) MIS capacitor by post-deposition annealing

In this study, we have fabricated a high-performance SiO2/β-Ga2O3 (001) MIS capacitor and investigated the effect of low-temperature post-deposition annealing (PDA) on its electrical properties. The SiO2/β-Ga2O3 (001) MIS capacitor exhibits improved gate leakage current and breakdown electrical field after the PDA treatment. The high-frequency capacitance-voltage hysteresis curves reveal that the fixed charge density, as well as the fast and deep near-interfacial trapped charge densities, decreases with the PDA process. We achieved an interfacial trapped charge density as low as 1.6 × 1011 cm−2 eV−1 at an energy of 0.6 eV below the conduction band of β-Ga2O3 (001) through 400 °C annealing.

(Invited) Role of Oxidant Gas for Atomic Layer Deposition of HfxZr1−XO2 Thin Films on Ferroelectricity of Metal-Ferroelectric-Metal Capacitors

Since the first report of ferroelectricity in HfxZr1−xO2 (HZO) in 2011 [1], a lot of attention has been devoted for future non-volatile memory device applications due to its scalability (< 10 nm), low thermal budget (< 400°C) and matured atomic layer deposition (ALD) technique [2]. The thermal ALD process using H2O or O3 is generally employed for the fabrication of ferroelectric HZO thin films. On the other hand, the effect of the plasma-enhanced ALD process using O2 plasma gas on the crystallinity and ferroelectricity has not been systematically clarified. In this paper, we report the importance of ALD oxidant gases for HZO films using H2O or O2 plasma on the ferroelectricity of metal–ferroelectric–metal (MFM) capacitors.MFM capacitors with the H2O- and O2 plasma-based HZO films were fabricated as follows. A 10-nm-thick HZO films were deposited on a TiN bottom-electrode (BE-TiN) by ALD at 300°C using H2O or O2 plasma as oxidant gases and (Hf/Zr)[N(C2H5)CH3]4 (Hf:Zr = 1:1) cocktail precursor. The Hf/Zr ratios in both types of HZO films were estimated to be 0.4/0.6 using X-ray photoelectron spectroscopy (XPS). Next, a post-deposition annealing (PDA) process was carried out at 400 °C for 1 min under a N2 atmosphere. Finally, a TiN top-electrode was deposited by DC sputtering.First, the crystallinity and remanent polarization (2P r = P r + − P r −) of the H2O- and O2 plasma-based HZO films were investigated. Nanocrystals with ferroelectric orthorhombic (O), tetragonal (T), cubic (C) phases partially existed in the O2 plasma-based film after the ALD process, while an amorphous structure dominantly existed in the H2O-based film, analyzed by the grazing-incidence X-ray diffraction analysis and cross-sectional transmission electron microscopy images [3]. This could be because of a strong oxidation power and high energy ion/electron bombardment of O2 plasma. After the PDA process, the O phase was formed more in the O2 plasma-based HZO film than the H2O-based film. Therefore, the nanocrystal grains in the as-grown O2 plasma-based HZO film could play an important role as nuclei for the crystallization and formation of O phase [3,4]. From the polarization–electric field hysteresis curves, the PDA-treated O2 plasma-based capacitor exhibited 2P r of 20 µC/cm2, which was 1.5 times higher than that (13 µC/cm2) of the H2O-based capacitor. Thus, these results indicate that the crystallization and O phase formation of HZO films were promoted by using O2 plasma gas as an ALD oxidant, resulted in a higher 2P r.Next, endurance properties of these MFM capacitors were evaluated. In the wake-up state, both capacitors showed almost the same increase rate (~8%) of switching polarization (P sw). In the fatigued state, on the other hand, the O2 plasma-based capacitor exhibited less P sw degradation (~33%) after 106 cycles, whereas the P sw of H2O-based capacitor decreased by ~47%. To clarify these different fatigue properties, the TiOxNy interface reaction layer (IRL) formation at the HZO/BE-TiN interface was analyzed using synchrotron hard X-ray photoelectron spectroscopy (HAXPES). For the HAXPES Ti 2p spectra, the Ti-O peak intensity for the O2 plasma-based capacitor was larger than that of the H2O-based capacitor [5]. Therefore, an oxygen-rich TiON-IRL could be formed at the HZO/BE-TiN interface during ALD process due to the stronger oxidizing power of O2 plasma. Additional oxygen vacancies (VO) were reported to formed in HfO2-based films during field cycling due to the interface reaction between the HfO2-based film and TiN electrode. Moreover, one of the origins of the P sw degradation was thought to be domain pinning caused by VO [6]. Therefore, an oxygen-rich TiON-IRL for the MFM capacitor with the O2 plasma-based HZO film could prevent the interface reaction and formation of additional VO in HZO films, led to superior fatigue properties.In summary, the MFM capacitor with the O2 plasma-based HZO film showed superior 2Pr and fatigue resistance compared to those of the H2O-based one. Based on these experimental results, it is important to consider the selection of an ALD oxidant for fabrication of HZO-based MFM capacitors.This work was partly supported by JSPS KAKENHI (Nos. JP21J01667, JP20H02189, and JP18J22998) and MEXT Leading Initiative for Excellent Young Researchers (No. JPMXS0320220213). The HAXPES measurements were performed under approval of the NIMS Synchrotron X-ray Station (2020A4602 and 2020A4651).[1] J. Müller et al., Appl. Phys. Lett. 99, 112901 (2011).[2] J.-H. Kim et al., ACS Appl. Electron. Mater. 5, 4726 (2023).[3] T. Onaya et al., APL Mater. 10, 051110 (2022).[4] T. Onaya et al., Microelectron. Eng. 215, 111013 (2019).[5] T. Onaya et al., Solid State Electron. 210, 108801 (2023).[6] M. Pešić et al., Adv. Funct. Mater. 26, 4601 (2016).

Impact of post deposition treatment on optoelectrical and microstructural properties of tin sulfide thin film for photovoltaic applications

Tin sulfide (SnS) has attracted significant interest due to its advantageous optoelectrical characteristics and abundant presence in nature. Post-deposition treatments (PDTs) are frequently employed to enhance the crystallinity of chalcogenide-based solar cells. This study examined the influence of the post-deposition heat treatment procedure on thermally evaporated SnS thin film. The post-deposition annealing process, as determined by XRD and AFM studies, supplies the necessary thermal energy for re-crystallization, potentially resulting in a modification of crystallite dimensions. The occurrence of Sn-S polytypes was examined using Raman and XPS studies. Annealing causes changes in the optical properties, as observed through optical analysis, which can be attributed to the improvement in crystallinity. Subjecting the material to annealing at temperature of 300 °C greatly improves both mobility and conductivity, while also causing a change in conduction type. The observed variations in conduction type are attributed to the differing ratios between the amounts of Sn2+ and Sn4+. This strategy offers a novel route for the fabrication of thin-film photovoltaic cells by using a p-type buffer layer.

Self-isolating electrode deposition process using the area-selective MoO2 and MoO3 atomic layer deposition technique

The traditional patterning process for semiconductor devices typically involves multiple steps, including thin film deposition across the entire substrate, selective removal of unwanted regions through lithography and etching, and subsequent isolation. While area-selective deposition process has been employed to eliminate the need for lithography and etching, the isolation step remains essential. In this study, we suggest an innovative approach to achieve “self-isolation electrode formation” using MoO2 and MoO3 as electrode and inter-metallic insulator materials. In a single deposition batch and subsequent post-deposition annealing (PDA) process, deposited MoOx (x: 2∼3) thin films exhibited transformation into highly crystalline MoO2 and MoO3 with low crystallinity, depending on whether they were deposited on TiN or SiO2 surfaces. We conducted comprehensive analyses, including chemical and electrical characterizations, as well as first-principles calculations based on density-functional theory, to elucidate the underlying mechanisms responsible for the differential reduction and crystallization of MoOx thin films. Finally, we successfully demonstrated the formation of self-isolation electrodes within a vertical structure, accomplished through a single-step process involving MoOx deposition and subsequent PDA. This novel approach, built upon advanced area-selective deposition techniques, holds great promise for the development of state-of-the-art semiconductor devices.

Improving the endurance for ferroelectric Hf0.5Zr0.5O2 thin films by interface and defect engineering

Improving the endurance performance for hafnia-based ferroelectric thin films and devices is of considerable significance from both scientific and technological perspectives. Here, we obtained robust ferroelectricity in Hf0.5Zr0.5O2 (HZO) thin films without the need of the confinement from top electrodes by systematically optimizing the conditions and parameters for the post-deposition annealing (PDA) process. Compared with the post-metallization annealing (PMA) process, PDA is found to markedly improve the ferroelectric endurance performance. In particular, wake-up-free ferroelectric HZO thin films with an exceptional endurance performance (∼3 × 1010 cycles) are obtained by PDA processing conducted under an oxygen atmosphere, which is attributed to the suppression of oxygen deficiency in the HZO thin films and the inhibition of interfacial reaction layer that inevitably forms during annealing treatment for PMA processing. Our work offers insight into improving ferroelectricity and endurance for hafnia-based ferroelectric materials and devices.

Hollow-cathode plasma deposited vanadium oxide films: Metal precursor influence on growth and material properties

Due to its different polymorphs, including vanadium pentoxide (V2O5) and vanadium dioxide (VO2), the vanadium oxide (VOX) compound is an immensely interesting material with many important applications. While atomic layer deposition (ALD) is among the possible VOX film synthesis methods, literature reports have majorly utilized thermal-ALD, which reveals as-grown amorphous VOX films. Further post-deposition annealing process is needed to crystallize these films. High-temperature crystallization indeed limits the use of low-temperature compatible materials, processes, and substrates. In this work, we report on the low-temperature crystalline VOX film growth in a hollow-cathode plasma-enhanced atomic layer deposition reactor using two different vanadium precursors, tetrakis(ethylmethylamino)vanadium and vanadium(V) oxytriisopropoxide. Oxygen plasmas were used as co-reactants at a substrate temperature of 150 °C. Along with the purpose of investing in the impact of metal precursors on VOX film growth, we also studied Ar-plasma in situ and thermal ex situ annealing to investigate possible structural enhancement and phase transformation. In situ Ar-plasma annealing was performed with 20 s, 20 SCCM Ar-plasma, while post-deposition ex situ annealing was carried out at 500 °C and 0.5 mTorr O2 pressure. In situ ellipsometry was performed to record instant film thickness variation and several ex situ characterizations were performed to extract the optical, structural, and electrical properties of the films. The outcomes of the study confirm that both metal precursors result in as-grown crystalline V2O5 films at 150 °C. On the other hand, post-deposition annealing converted the as-grown crystalline V2O5 film to VO2 film. Finally, we have also successfully confirmed the metal-to-insulator transition property of the annealed VO2 films via temperature-dependent structural and electrical measurements.

Enhanced temperature coefficient of resistance of VOX-based uncooled microbolometers manufactured by plasma enhanced atomic layer deposition

Vanadium oxide (VOX) is a promising material for developing the sensor film of uncooled microbolometers. However, amorphous VOX film, which is typically formed on the Si substrate, is unstable due to ambient unwanted oxidation in air, making their resistance too high to be employed in microbolometers. Therefore, studies on improving the quality and stability of VOx film are still ongoing. This study presents our strategies based on plasma-enhanced atomic layer deposition (PEALD) and rapid thermal annealing (RTA) for manufacturing VOx films with high crystallization and stability. The VOx sensing layer for microbolometers was fabricated at a low process temperature of 370 °C using NH3 gas, and the rapid thermal anneal was performed as the essential post-deposition annealing process for improving the VOx crystallization. Besides, in-situ deposition of an Al2O3 layer on the VOx film improves its stability. Compared with a bare VOx film, our developed Al2O3/VOx film shows an improvement of −3.5%/K in the temperature range of 298–328 K. For the optimized sample, changes in the electrical, chemical, and surface characteristics of the VOx film due to Al2O3 or Al-doping are studied and discussed in detail to find the mechanism of that improvement.

Post-deposition annealing process as a defect-driven tool for tuning the chemical and electron properties of sol–gel spin-coated aluminium oxide thin layers

Within current work we present the impact of annealing temperature on the chemical and electron properties of alumina thin layered samples prepared by sol–gel method followed by spin-coating deposition. The determination of the impact was based on the comprehensive photoelectron spectroscopies investigations in X and UV range. Examinations were supported by the simulated density of states spectra that served also as a support for defect energy level assignment in the valence band region from X-ray photoelectron spectroscopy data. Moreover, the quality of the layers was additionally monitored with atomic force microscopy. We demonstrate that our technology results in continuous, homogenous and smooth layers of controlled stoichiometry. Our approach allows direct control of the chemical and electronic structure (e.g. work function, Wf, ionization energy, IE) with post-deposition temperature processing. We show that oxygen vacancies induced by temperature treatment are the main driving force changing the electronic structure. The control of the Wf and IE is possible in annealing conditions above 800 °C. Finally, we analyse carbon contamination impact on the obtained layers’ structure. Our findings may have a direct impact on the engineering of modern oxide-based electronics enabling cost reduction and more precise control of aluminium oxide layers–based devices.

Vanadium oxide thin film deposited on Si by atomic layer deposition for non-volatile resistive switching memory devices

Vanadium dioxide (VO2) is a representative metal–insulator-transition (MIT) material that undergoes a reversible phase transition at 68 °C, which is close to room temperature. This shows the bias-triggered volatile resistance changes driven by MIT so that many studies have been made to implant VO2 as selectors for solving the sneak current problem of resistive random-access memory (ReRAM). However, the non-volatile switching of VO2 for non-volatile memory (NVM) application has not been demonstrated yet but if realized, this is truly breakthrough for low power and ultrafast NVM application. Herein, we report a successful formation of multiphase vanadium oxide on Si wafer via atomic layer deposition followed by a post-deposition annealing (PDA) process and demonstrate its applicability as a NVM device. It was confirmed that the multiphase vanadium oxide has MIT-driven abrupt resistance switching (i.e., low- and high-resistance state) at ± 1.6 V due to increased oxygen vacancies responsible for non-volatile memory property. The alternating current (AC) endurance upto 30,000 cycles and charge retention upto 3,000 sec are achieved at 2ⅹ102 of LRS/HRS current ratio. As a result, it opens the possibility of application to next-generation memory devices by reliable non-volatile MIT switching scheme.

Improved ferroelectric properties of CMOS back-end-of-line compatible Hf0.5Zr0.5O2 thin films by introducing dielectric layers

Hf0.5Zr0.5O2 (HZO) ferroelectric thin films have gained significant attention for the development of next-generation ferroelectric memories by complementary-metal-oxide semiconductor (CMOS) back-end-of-line (BEOL) processing, due to their relatively low crystallization temperature. However, it remains challenging to achieve excellent ferroelectric properties with post deposition annealing (PDA) process at a BEOL compatible temperature. Along these lines, in this work, it is demonstrated that the ferroelectricity of 15 nm thick HZO thin film prepared by PDA process at 400 °C can be improved to varying degrees, via depositing 2 nm thick dielectric layers of Al2O3, HfO2, or ZrO2 at either the bottom or the top of the film. Notably, the HZO thin film with the top-Al2O3 layer exhibits remarkable ferroelectric properties, which are independent of the thickness of HZO. The 6 nm thick HZO thin film shows a total remanent polarization (2Pr) of 31 μC/cm2 under an operating voltage of 2.5 V. These results represent a significant advancement in the fabrication of high-performance, BEOL compatible ferroelectric memories, as compared to previously reported state-of-the-art works.

Forming-Free HfOx-Based Resistive Memory With Improved Uniformity Achieved by the Thermal Annealing-Induced Self-Doping of Ge

In this work, a forming-free HfOx-based resistive random access memory (RRAM) with improved uniformity is successfully demonstrated without an additional doping process, ionic injection, or special layer deposition. The significantly enhanced performances can be attributed to the self-doping of Ge atoms from the Ge bottom electrode (BE) into the HfO2 layer during the postdeposition annealing (PDA) process. Besides, the RRAM provides a lower reset current and a higher ON/OFF ratio than the reported forming-free RRAM. These excellent properties are beneficial to the application of power-saving RRAM and its circuit operation.

Impact of annealing on material and electrical characteristics of lithium phosphate thin films on silicon carbide

In this study, we investigated the influence of post-deposition annealing (PDA) process on lithium phosphate (Li3PO4) solid-state thin films on silicon carbide (SiC) substrate in terms of materials and electrical properties. Li3PO4 thin films were deposited through radio frequency (RF) sputtering and post-deposition annealing was performed in a temperature range of 200–400 °C. The Li3PO4 thin films show typical amorphous structures, and no changes are observed even after 400 °C PDA process. The Li 1 s/P 2p ratio varies with changing the annealing temperature and the highest Li is detected under 300 °C annealing, where the ionic conductivity increases to 1.00 × 10−4 S/mm at the same temperature. The rectification ratio of the 300 °C annealed device is obtained as 1.45 × 103, which is 23 times higher value than as-deposited Li3PO4/SiC device without annealing. This result suggests that the delicate control of Li3PO4 deposition could provide a significant enhancement on the electrical devices and the solid electrolyte batteries.

Hydrogen-Doping-Enabled Boosting of the Carrier Mobility and Stability in Amorphous IGZTO Transistors.

This study investigated the effect of hydrogen (H) on the performance of amorphous In-Ga-Zn-Sn oxide (a-In0.29Ga0.35Zn0.11Sn0.25O) thin-film transistors (TFTs). Ample H in plasma-enhanced atomic layer deposition (PEALD)-derived SiO2 can diffuse into the underlying a-IGZTO film during the postdeposition annealing (PDA) process, which affects the electrical properties of the resulting TFTs due to its donor behavior in the a-IGZTO. The a-In0.29Ga0.35Zn0.11Sn0.25O TFTs at the PDA temperature of 400 °C exhibited a remarkably higher field-effect mobility (μFE) of 85.9 cm2/Vs, a subthreshold gate swing (SS) of 0.33 V/decade, a threshold voltage (VTH) of -0.49 V, and an ION/OFF ratio of ∼108; these values are superior compared to those of unpassivated a-In0.29Ga0.35Zn0.11Sn0.25O TFTs (μFE = 23.3 cm2/Vs, SS = 0.36 V/decade, and VTH = -3.33 V). In addition, the passivated a-In0.29Ga0.35Zn0.11Sn0.25O TFTs had good stability against the external gate bias duration. This performance change can be attributed to the substitutional H doping into oxygen sites (HO) leading to a boost in ne and μFE. In contrast, the beneficial HO effect was barely observed for amorphous indium gallium zinc oxide (a-IGZO) TFTs, suggesting that the hydrogen-doping-enabled boosting of a-IGZTO TFTs is strongly related to the existence of Sn cations. Electronic calculations of VO and HO using density functional theory (DFT) were performed to explain this disparity. The introduction of SnO2 in a-IGZO is predicted to cause a conversion from shallow VO to deep VO due to the lower formation energy of deep VO, which is effectively created around Sn cations. The formation of HO by H doping in the IGZTO facilitates the efficient connection of atomic states forming the conduction band more smoothly. This reduces the effective mass and enhances the carrier mobility.

(Digital Presentation) Photonic Curing of Hybrid Transparent Electrodes for High-Throughput Solar Cell Manufacturing

Realizing high-throughput, low-cost perovskite solar cell (PSC) manufacturing is highly sought-after in photovoltaic research in recent years. PSCs can be fabricated using inexpensive and scalable solution-deposition methods, such as slot-die coating, blade coating, or spray coating, that can be performed in open air or under inert gas conditions and are compatible with high-throughput, roll-to-roll (R2R) manufacturing. To fully achieve R2R manufacturing of PSCs, it is important to also consider the flexible transparent electrode (TE). PET/ITO is a commonly used substrate for making flexible PSCs. When optimizing transparent conducting materials, there is a tradeoff between sheet resistance (Rsh) and optical transparency. PET/ITO substrates with high Rsh have high transparency and smoother ITO surfaces, compared to PET/ITO substrates with low Rsh, which have low transparency and higher surface roughness, indicating thicker ITO films. ITO is brittle and tends to crack under mechanical stress or bending, which is further exacerbated when using a thicker ITO layer. It is desired to have a thin ITO film with low Rsh, high optical transparency, and smooth surface roughness. Because commercial PET/ITO substrates are made with slow (~1 m/min) vacuum deposition processes, they tend to be expensive. Therefore, it would be advantageous to develop a high-throughput, R2R compatible, solution-deposition approach for fabricating the TE on PET substrates. To achieve this, two key processes must be developed: A solution-deposition process that enables uniform coating of the TE on PET and a post-deposition annealing process that is compatible with the low-temperature PET and high speed of R2R manufacturing. While various solution-deposition processes, such as those listed above, can achieve the desired web speed of > 30 m/min, there is still a need to improve the post-deposition annealing step.One promising post-deposition processing technique is intense-pulsed-light processing, also known as photonic curing. Photonic curing delivers short (0.01 – 100 ms) pulses of broadband (200 – 1500 nm) light from a xenon flash lamp to the samples. Any materials in the sample stack that absorb light will convert the impinging light pulse into heat within the sample, which drives changes in the sample (calcination, phase change, crystallization, etc.). Photonic curing has three main advantages over thermal annealing: 1. Faster processing speed (milliseconds or seconds). 2. Compatibility with plastic substrates. 3. Smaller physical footprint and less wasted energy. Since the light pulses are on for a short time, the intensity can be high while the total energy delivered to the sample is low. During the photonic curing process, the absorbed light causes the TE precursor film to selectively and quickly (microseconds – milliseconds) heat up, while the PET substrate underneath heats up less and slower (seconds). Because the thin film is a few orders-of-magnitude thinner than the PET substrate, the heat generated and transferred from the thin film does not cause significant substrate heating. This allows high-temperature processing in the top layers of the sample stack, while keeping the bottom plastic substrate temperature low.In this work, a hybrid TE material is fabricated on PET substrates using photonic curing. The hybrid TE material contains a layer of silver nanowires (AgNWs) and a layer of metal-oxide (ITO, IZO, etc.). The AgNWs increase the light absorbed by the film during the photonic curing process, which leads to higher processing temperatures, possibly improving the conversion of the metal-oxide layer. The AgNWs also enhance the electrical conductivity of the final TE layer after photonic curing. A AgNW and metal-oxide bilayer is formed by spin coating each solution onto the PET substrate sequentially followed by a single photonic curing process. We use average optical transmittance (Tavg) from 400 to 700 nm and average Rsh to evaluate the TE performance. The following photonic curing parameters are varied to optimize Tavg (maximize) and Rsh (minimize): Pulse voltage, pulse envelope, number of micro-pulses, duty cycle, number of pulses, and pulse repetition rate. Preliminarily, we also observe a significant impact on the TE properties by the volume of AgNW deposited during the spin coating deposition step. Using dispense volumes of 80 µL and 20 µL, we achieve samples with Tavg = 73%, Rsh = 19 Ω/sq, and roughness = 9 nm, and Tavg = 83%, Rsh = 58 Ω/sq, and roughness = 5.6 nm, respectively, after photonic curing. Fig. 1 a-d shows SEM, AFM, sample schematic, and AFM line-cuts of the photonic cured hybrid TE sample, respectively. Figure 1

Effect of Post-Deposition Annealing on the Structural Evolution and Optoelectronic Properties of In2O3:H Thin Films.

An infrared transparent conductive material is a solution to realize the shielding function of infrared windows against electromagnetic waves, by combining the two characteristics of high transmission and conductivity in infrared wavelengths. Indium-hydroxide-doped (In2O3:H) thin films were prepared by atomic layer deposition method, which can achieve high IR transmission by reducing the carrier concentration on the basis of ensuring the electrical properties. On this basis, the effect of the post-deposition annealing process on the microstructure evolution and optoelectronic properties of In2O3:H thin films was investigated in this paper. It is demonstrated that the carrier mobility after annealing is up to 90 cm2/(V·s), and the transmittance at the 4 μm is about 70%, meanwhile, the carrier concentration after annealing in air atmosphere is reduced to 1019 cm−3, with a transmission rate of up to 83% at 4 μm. The simulations visualize the shielding performance of the annealed In2O3:H thin film against radar electromagnetic waves. It provides a guideline for fabricating lightweight, thin, and multi-functional shielding infrared transparent materials in the key fields of spacecraft and high precision electronics.

Influence of post-deposition annealing on the novel alloyed SnSxO1-x semiconductor in p-type thin-film transistors

SnO is an oxide semiconductor that has the potential to be used in the development of thin-film transistors (TFTs) with a p-type channel. SnO on the other hand is a metastable phase, and the oxidation of the SnO films makes high-performance TFTs with good mobility and high on/off current ratios challenging. In this study, based on the SnO–SnO2 phase transformation mechanism, a novel alloyed semiconductor SnSxO1-x was reported to prevent the conversion of SnO to SnO2. Pulsed laser deposition was used to grow SnO and SnSxO1-x thin films on Si/SiO2 substrates, which were then exposed to rapid annealing procedures. From Raman spectroscopic analysis, SnSxO1-x exhibited better antioxidant performance than pure SnO at the same post-deposition annealing process. The developed SnSxO1-x TFTs exhibited better stability and an improved on/off ratio than SnO TFTs after high-temperature annealing. Additionally, we fabricated bilayer SnSxO1-x/SnO thin-film transistors with typical p-channel conduction and a 10−11 A off-state current.

Integration of Ferroelectric K0.5Na0.5NbO3 films on Si at 400 ℃

In this work, polycrystalline K0.5Na0.5NbO3 (KNN) thin films were successfully integrated on Si at 400 ℃ via a RF magnetron sputtering process. These films showed a polycrystalline bulk-like orthorhombic phase with mixed (00l) and (110) orientations, as was supported by X-ray diffraction and piezoelectric force microscopy analyses. Without a post-deposition annealing process, these films already showed a clear ferroelectric polarization-electric field (P-E) hysteresis loop, characterized by a remnant polarization ~11μC/cm2 and a coercive field of ~280 kV/cm. This polarization response shows a good aging resistance (~2 years). A dielectric constant of ~230 and a low loss tangent of ~1.8 % (@1 kHz) were achieved in the KNN film. Lastly, large dielectric tunabilities of ~50 % (@ 1 MHz) was revealed for the KNN film, illustrating their good potential for applications in tunable dielectrics.

Effect of 2 MHz frequency power applied to the substrate for low-temperature silicon nitride thin film deposition

Silicon nitride (SiNx) thin films were deposited at a low temperature of 80 °C using a dual-frequency plasma-enhanced chemical vapor deposition (PECVD) equipment. The density of the thin film was increased by 17% by increasing the low-frequency (LF) power of 2 MHz applied to the lower electrode to 100 W separately from the plasma generated by the 180 W power of 13.56 MHz applied to the upper electrode. The advantage of this dual-frequency PECVD process is that even if it is deposited at a low temperature, it shows similar effects to high-temperature deposition or post-deposition annealing process. Due to the LF power applied to the substrate, the hydrogen concentration in the deposited SiNx thin film decreases, which in turn leads to an increase in the film density. The increase in SiNx thin film density eventually results in a 21% increase in dielectric constant. It was shown that the use of SiNx thin films with improved properties as a dielectric layer of a thin film transistor can increase mobility and on-off ratio and reduce leakage current and subthreshold swing of the transistor.

Interface optimization of La-based gate dielectric for molybdenum disulfide field-effect transistors

Two-dimensional (2D) layered materials such as graphene, transition metal dichalcogenides are considered as the promising candidates for new generation electronics and optoelectronics, owing to their unique physical properties and abundant design freedom. However, the problem of heterogeneous integration of two-dimensional materials with gate dielectric materials has not been solved, especially the problem of interface qualities, which limits the development of two-dimensional electronics. Herein, we demonstrate the feasibility of interface optimization through post-deposition annealing process. The proposed La-based oxide MoS2 transistor offers high mobility of 60 cm2/V·s, increased by 136% up to ∼ 50uA/um and low interface trap density after post-deposition annealing treatment. The detailed research results show that N2 atmosphere annealing treatment can not only promote the composition of LaAlO3, but also suppress the Coulomb scattering generated from interface state charge. All these results provide an enhanced fabrication scheme for heterogeneous integration with the optimized interface and offer reference for high-reliability manufacturing of low-power two-dimensional electronic devices.

Enhancement of Electrical Properties of Sol-Gel Indium-Tin-Oxide Films by Microwave Irradiation and Plasma Treatment.

We proposed the enhancement of the electrical properties of solution-processed indium–tin–oxide (ITO) thin films through microwave irradiation (MWI) and argon (Ar) gas plasma treatment. A cost- and time-effective heat treatment through MWI was applied as a post-deposition annealing (PDA) process to spin-coated ITO thin films. Subsequently, the sheet resistance of MWI ITO thin films was evaluated before and after plasma treatment. The change in the sheet resistance demonstrated that MWI PDA and Ar plasma treatment significantly improved the electrical properties of the ITO thin films. Furthermore, X-ray photoelectron spectroscopy and X-ray diffraction analyses showed that the electrical properties of the ITO thin films were enhanced by the increase in oxygen vacancies due to the ion bombardment effect of high-energy plasma ions during Ar plasma treatment. Changes in the band gap structure of the ITO thin film due to the ion bombardment effect were also analyzed. The combination of MWI PDA and Ar plasma treatment presents new possibilities for improving the high-conductivity sol–gel ITO electrode.