CF4 Plasma Treatment Research Articles

Improving bias stability of IGZO field-effect transistors through CF4 plasma treatment of Al2O3 dielectrics

In this study, the effects of the CF4 plasma treatment on the amorphous indium gallium zinc oxide (IGZO) material were explored. The electrical characteristics of the IGZO-based field-effect transistor (FET) were also thoroughly examined to analyze the influence of the plasma treatment. Excellent adhesion of the sol-gel-based IGZO semiconducting film was achieved owing to the strong dipole moment of the AlOxFy layer created by the surface treatment. In particular, X-ray photoelectron spectroscopy depth profiles and transmission electron microscopy electron energy loss spectroscopy analyses provided clear evidence that fluorine atoms diffused into the Al2O3 surface via the CF4 plasma treatment. The formation of an AlOxFy layer at the IGZO/Al2O3 interface is expected to be advantageous for reducing the interface trap density, thereby enhancing the critical transistor parameters. Additionally, the plasma-treated IGZO transistor demonstrated strong electrical bias stability under continuous gate bias stress conditions. Therefore, surface modification via CF4 plasma treatment is proposed to boost the stability and performance of the device, offering a straightforward approach for integrated thin-film transistor circuitry in advanced display applications.

Hydrogen evolution coupled with microplastic upcycling in seawater via solvent-free plasma F-functionalized CoNi alloy catalysts

The deleterious impacts of marine polyethylene terephthalate (PET) microplastic pollution on aquatic organisms have garnered global concern. Crafting a more cost-effective method to derive high value-added products from these microplastics is a pivotal challenge in marine resource reuse. This study introduces a strategy for electrooxidation of PET microplastics coupled with seawater electrolysis for green hydrogen production, resulting in value-added chemical formic acid at the anode and hydrogen gas at the cathode. Specifically, a catalyst composed of carbon nanotube-interconnected CoNi alloy-loaded carbon nanocages was fabricated, and F were doped onto the catalyst surface via solvent-free CF4 plasma treatment. Owing to its unique hollow 1D/3D interconnected structure, the synergistic effect of the CoNi alloy, and the ease of reconstruction of metal-F bonds in an alkaline environment, the prepared electrocatalyst exhibited excellent performance in the hydrogen evolution reaction and oxygen evolution reaction, the current density of 10 mA cm−2 was obtained at the overpotential of 187 mV and 315 mV, respectively. Furthermore, the proposed coupling strategy achieved a potential saving of 165 mV at a current density of 10 mA cm−2. This research offers promising prospects for the development of “marine hydrogen mining” and the management of ocean microplastics.

Synergistic effect of reducing volume expansion and improving electrochemical performance through a LiF-based SEI formation on SiOx/C electrodes

SiOx/C electrodes are widely used due to their high lithium storage capacities and cycling stabilities. However, the SiOx/C electrode exhibits large volume expansion and unstable SEI layer formation during cycling. In this work, a carbon tetrafluoride (CF4) plasma was used to introduce C-F bonds onto the electrode surface to form a LiF-based SEI layer on a SiOx/C electrode (SGE) to improve its mechanical and electrochemical properties. The fluorinated SiOx/C electrode (FSGE) subjected to the CF4 plasma treatment for 10 min mitigated 2.5 times the volume expansion compared to the SGE by forming a LiF-based SEI layer to increase the mechanical properties. This mitigation of FSGE volume expansion resulted in excellent long-term cycling stability of 83 % for 100 cycles (1C). In addition, the LiF-based SEI layer formed on the FSGE increased the mobility of Li ions, resulting in 1.2 times better cycle stability than that of SGE at a high rate (10C). Thus, the improvement in the electrochemical performance achieved by reducing the volume expansion of SiOx in the electrode and enhancing the Li-ion conductivity was attributed to the stable LiF SEI layer formed with semi-ionic CF bonds introduced by the CF4 plasma.

Multi-scale modified PVDF/Ag@C layer based on dielectric doping and plasma treatment for high-performance triboelectric nanogenerators and self-powered water sterilization

The limitations of dielectric properties and surface electron affinity and the harsh environment including high humidity, high salt content, and biological fouling restricted the efficient ocean energy harvesting of triboelectric nanogenerators (TENGs). Here, Ag@C dielectric doping and two-step O2+CF4 plasma treatment are applied to achieve multi-scale modification of triboelectric materials. The coating of C shell avoided the agglomeration of Ag NPs. Besides, the amorphous C shell inhibited the formation of electron transport pathways, and the mechanism of suppressing dielectric loss of triboelectric layers were clarified via DFT calculations at the particle (Ag@C)-polymer (polyvinylidene difluoride, PVDF) interface. The surface charge density of plasma treated polyvinyl alcohol (PVA)-PVDF/Ag@C-based TENG (PT-TENG) increased from 64.26 µC/m2 to 216.60 µC/m2, representing a significant breakthrough in energy harvesting efficiency. The mechanism of enhanced triboelectric properties was investigated based on modified Overlapped Electron Cloud model. Besides, DFT was applied to analyze the reaction mechanism in depth and predict the products of chemically-surface modification process. The oxygen-containing functional groups introduced by O2 plasma treatment likely serve as a "bridge" for the second-step grafting, which helps to build a more convincing reaction mechanism. The superhydrophobic PVDF/Ag@C exhibited excellent moisture-resistance, salt-resistance, and anti-bioadhensive properties, with outstanding charge density (321.45 µC/m2) at 95% RH, making it very suitable for energy harvesting in harsh marine environments. Moreover, the water sterilization system based on PT-TENG demonstrated a high sterilization rate of 98.74%, which was significantly higher than conventional AC power (89.96%).

MoS2 Field-Effect Transistor Performance Enhancement by Contact Doping and Defect Passivation via Fluorine Ions and Its Cyclic Field-Assisted Activation.

MoS2-based field-effect transistors (FETs) and, in general, transition metal dichalcogenide channels are fundamentally limited by high contact resistance (RC) and intrinsic defects, which results in low drive current and lower carrier mobilities, respectively. This work addresses these issues using a technique based on CF4 plasma treatment in the contacts and further cyclic field-assisted drift and activation of the fluorine ions (F-), which get introduced into the contact region during the CF4 plasma treatment. The F- ions are activated using cyclic pulses applied across the source-drain (S/D) contacts, which leads to their migration to the contact edges via the channel. Further, using ab initio molecular dynamics and density functional theory simulations, these F- ions are found to bond at sulfur (S) vacancies, resulting in their passivation and n-type doping in the channel and near the S/D contacts. An increase in doping results in the narrowing of the Schottky barrier width and a reduction in RC by ∼90%. Additionally, the passivation of S vacancies in the channel enhances the mobility of the FET by ∼150%. The CF4 plasma treatment in contacts and further cyclic field-assisted activation of F- ions resulted in an ON-current (ION) improvement by ∼90% and ∼480% for exfoliated and CVD-grown MoS2, respectively. Moreover, this improvement in ION has been achieved without any deterioration in the ION/IOFF, which was found to be >7-8 orders.

The Influence of UV-Ozone, O2 Plasma, and CF4 Plasma Treatment on the Droplet-Based Deposition of Diamond Nanoparticles.

Surface treatment is critical for homogeneous coating over a large area and high-resolution patterning of nanodiamond (ND) particles. To optimize the interaction between the surface of a substrate and the colloid of ND particles, it is essential to remove hydrocarbon contamination by surface treatment and to increase the surface energy of the substrate, hence improving the diamond film homogeneity upon its deposition. However, the impact of substrate surface treatment on the properties of coatings and patterns is not fully understood. This study explores the impact of UV-ozone, O2 plasma, and CF4 plasma treatments on the wetting properties of the fused silica glass substrate surface. We identify the optimal time interval between the treatment and subsequent ND coating/patterning processes, which were conducted using inkjet printing and ultrasonic spray coating techniques. Our results showed that UV-ozone and O2 plasma resulted in hydrophilic surfaces, while CF4 plasma treatment resulted in hydrophobic surfaces. We demonstrate the use of CF4 plasma treatment before inkjet printing to generate high-resolution patterns with dots as small as 30 μm in diameter. Ultrasonic spray coating showed homogeneous coatings after using UV-ozone and O2 plasma treatment. The findings of this study provide valuable insights into the hydrocarbon airborne contamination on cleaned surfaces over time even in clean-room environments and have a notable impact on the performance of liquid coatings and patterns. We highlight the importance of timing between the surface treatment and printing in achieving high resolution or homogeneity.

Enhancement of hydrophobic properties of HTV silicone rubber by CF4 plasma treatment

In this paper, a superhydrophobic surface of silicone rubber was fabricated by plasma treatment method. Modification of the surface chemistry under CF4 atmosphere at different times (3, 5, and 7 min) and powers (50, 75, and 100 W) of plasma process has been investigated. A superhydrophobic surface with contact angle of 151.3° was obtained for plasma treated sample at 100 W for 7 min. X-ray photoelectron spectroscopy (XPS) results indicated that the surface fluorination of silicone rubber increased as the time and power of plasma exposure increased. Investigation of the F 1s and Si 2p spectra approved the formation of F-C and F-Si bands. Also, the roughness of the surface increased from about 42 nm for untreated to 55 nm for treated sample (7 min at 100 W) due to the emergence of the ceramic fillers in degraded silicone rubber matrix after plasma treatment. Both of the surface fluorination and roughness increment are the reasons of superhydrophobicity properties. Examination of the hydrophobic recovery by surface contamination method indicated that a contact angle of 101° was recovered after 9 days.

Force-Based Characterization of the Wetting Properties of LDPE Surfaces Treated with CF4 and H2 Plasmas.

Low-density polyethylene (LDPE) films are widely used in packaging, insulation and many other commodity applications due to their excellent mechanical and chemical properties. However, the water-wetting and water-repellant properties of these films are insufficient for certain applications. In this study, bare LDPE and textured LDPE (T-LDPE) films were subjected to low-pressure plasmas, such as carbon tetrafluoride (CF4) and hydrogen (H2), to see the effect of plasma treatment on the wetting properties of LDPE films. In addition, the surface of the LDPE film was textured to improve the hydrophobicity through the lotus effect. The LDPE and T-LDPE films had contact angle (θ) values of 98.6° ± 0.6 and 143.6° ± 1.0, respectively. After CF4 plasma treatments, the θ values of the surfaces increased for both surfaces, albeit within the standard deviation for the T-LDPE film. On the other hand, the contact angle values after H2 plasma treatment decreased for both surfaces. The surface energy measurements supported the changes in the contact angle values: exposure to H2 plasma decreased the contact angle, while exposure to CF4 plasma increased the contact angle. Kinetic friction force measurements of water drops on LDPE and T-LDPE films showed a decrease in friction after the CF4 plasma treatment, consistent with the contact angle and surface energy measurements. Notably, the kinetic friction force measurements proved to be more sensitive compared to the contact angle measurements in differentiating the wetting properties of the T-LDPE versus 3× CF4-plasma-treated LDPE films. Based on Atomic Force Microscopy (AFM) images of the flat LDPE samples, the 3× CF4 plasma treatment did not significantly change the surface morphology or roughness. However, in the case of the T-LDPE samples, Scanning Electron Microscopy (SEM) images showed noticeable morphological changes, which were more significant at sharp edges of the surface structures.

Current Drops in CF4 Plasma-Treated AlGaN/GaN Heterojunction in Polar Gas Ambient

This letter reports the phenomenon of current drops in an AlGaN/GaN heterojunction with CF4 plasma treated in a polar gas ambient. Ungated AlGaN/GaN HEMT with CF4 plasma treatment was tested in ethanol, acetonitrile, and an acetic acid gas ambient, and the current dropped by 52%, 51% and 61%, respectively, which are much higher than the drops (6%, 7%, and 8%) in normal ungated HEMT. On the one hand, based on “ambient doping”, a possible model was proposed to explain this phenomenon. On the other hand, the lower initial current was very important to increase the sensitivity. This means that the initial current should be elaborately designed to achieve maximum sensitivity.

Low-pressure plasma treated polycarbonate and polymethyl methacrylate (PMMA) sheets with different surface patterns to change their surface properties

Low-pressure plasmas of carbon tetrafluoride (CF4), oxygen (O2), and air were used to treat the surfaces of polycarbonate (PC) and polymethyl methacrylate (PMMA) to achieve a variety of surface attributes, such as hydrophilicity, hydrophobicity, and surface free energy. Patterns of straight line, triangular and square shapes with different sizes e.g., 0.5 mm, 0.75 mm, and 1 mm dimensions as templates were constructed from stainless-steel sheets with a thickness of 1 mm, via laser cutter, were used to induce the corresponding shape of the functionality on PC and PMMA surfaces during plasma gas treatment were also investigated. The untreated PC and PMMA surfaces have a contact angle (θ) value of 70°±0.47° and 77°±0.80°, respectively. As expected upon CF4 plasma treatment, their contact angle values were increased to 109.04°±0.35° and 105.76°±0.61°, respectively; whereas the air plasma treated surfaces became more hydrophilic with the contact angle values of 29.34°±0.14° and 43.99°±0.22°, correspondingly. Moreover, O2 plasma treated surfaces became more hydrophilic with the contact angle values of 25.32°±0.77° for PC and 39.94°±2.05° for PMMA. Also, surface free energy (SFE) values were decreased to 11±0.87 mN/m from 41.16±0.42 mN/m for PC and to 12.11±1.53 mN/m from 35.93±1.12 mN/m for PMMA upon CF4 treated surfaces. Furthermore, SFE values were increased to 57.59±1.12 and 62.13±1.15 mN/m for PC and PMMA after air plasma treatment. PC surface's, advancing and receding contact angles were determined as 101.48°±0.33° and 65.60°±0.11° respectively for 34.77°±0.50° slide-off angles. Moreover, the advancing and receding contact angles for PMMA were found as 93°±0.64° and 61.60°±1.19°, respectively with a sliding angle of 24.49°±1.14°. X-ray Photoelectron Spectroscopy (XPS) analysis results confirmed the fluorination and oxidation of both PC and PMMA after CF4 and O2 plasma treatments, individually. PC and PMMA surfaces were treated multiple times with CF4 and Air, Air and CF4, O2 and CF4, and CF4 and O2 plasmas in succession. After multiple treatment, PC and PMMA surfaces contact angle values were decreased as low as 10.62°±0.88° and 14.96°±0.2°, respectively.

Controlling the Surface Modification by CF4 Plasma Treatment for Inkjet Printed Color Conversion Layer With InP‐Based QDs Ink

AbstractControlling of thickness profile in micro‐scale pixels via an inkjet printing process remains a challenge and strict control of surface energy is required. Herein, the surface energy of each substrate is controlled by using CF4 plasma treatment (CPT) to control thickness profile and improve color conversion efficiency (CCE) of the inkjet printed quantum dots (QDs) color conversion layer (CCL). The bank surface becomes hydrophobic due to the fluorination, while the glass becomes hydrophilic due to the cleaning effect by the CPT. Through a systemic investigation of the polar and non‐polar components of the surface energy, it is found that the ink behavior of inkjet‐printed QDs in the pixels is closely related to the non‐polar component of the surface energy. In addition, it is found that more rigorous control of the surface is required for array printing and a wide range of thickness profile control is possible by CPT. The thickness increases by up to 10 µm, the blue leakage is reduced by 26.38%, and the CCE increases by a maximum of 5.71% depending on the CPT. As a result, the relationship between the thickness profile of the CCL and CCE is confirmed through the fabrication of QD‐organic light emitting diodes.

Surface Modification of a Regenerated Cellulose Film Using Low-Pressure Plasma Treatment with Various Reactive Gases.

There is a growing interest in the fabrication of membranes and packaging materials from natural resources for a sustainable society. A regenerated cellulose (RC) film composed solely of cellulose has outstanding advantages including biodegradability, transparency, mechanical strength, and thermal stability. To expand the application of the RC film, various surface modification methods have been proposed. However, conventional chemical methods have disadvantages such as environmental burden and difficulty in controlling the reaction. In this work, low-pressure plasma treatment, a green, solvent-free, and easily controllable approach, was performed for surface modification of the RC film. The effects of three different plasma species (O2, N2, and CF4) and treatment conditions on the surface properties of RC films were investigated based on water contact angle measurements, chemical composition analysis, and surface topography. O2 and N2 plasma treatment slightly enhanced the surface wettability of RC films due to the etching by the plasma reactive species and the formation of new hydrophilic functional groups. In CF4 plasma treatments, the hydrophobic surface with a contact angle of 120.6° was obtained in a short treatment time (60 s) owing to the deposition of fluorocarbon groups on the surface. However, the treated surface in a longer reaction time resulted in increased wettability due to the diffusion and degradation of fluorine-containing bonds. The new insights could be valuable for further studies of surface modification and functionalization of RC films.

First demonstration of hetero-epitaxial ε-Ga2O3 MOSFETs by MOCVD and a F-plasma surface doping

This letter reports on the demonstration of ε-phase gallium oxide (ε-Ga2O3) based metal-oxidesemiconductor field effect transistors (MOSFETs) for the first time. Phase-pure ε-Ga2O3 film was hetero-epitaxially grown on a sapphire substrate by metal organic chemical vapor deposition (MOCVD) using a two-step growth method. The high crystalline quality of the epilayer was confirmed with the X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) investigations. Through a proper surface cleaning and CF4-plasma treatment process, fluorine (F) atoms were incorporated and acted as donors in the ε-Ga2O3 film, by which the sheet resistance (Rsh) of the epilayer was decreased by 105. Based on this F-plasma doped ε-Ga2O3 film, MOSFETs with a maximum output current density exceeding 3 mA/mm were successfully demonstrated. The doping profile extracted from the capacitance-voltage (C-V) measurement showed a significant carrier accumulation near the ε-Ga2O3 film surface with a peak concentration of 5 × 1017 cm−3 and an integrated carrier density of ∼6.4 × 1011 cm−2. The peak electron effective mobility (μeff) within the MOSFET channel was extracted to be as high as 19 cm2/Vs, indicating a great potential of ε-Ga2O3 based electronics for future high-speed and high-power applications.

Stabilizing the Energy Harvesting of PVDF‐Fabric‐Based TENGs Exposed to Moisture and Dust Particles by O2 and CF4 Plasma Treatments

AbstractSuperhydrophobic polyvinylidene fluoride (PVDF) fabrics comprising electrospun PVDF yarns are developed via O2 and CF4 plasma treatments to achieve stable triboelectric energy harvesting performance. The dynamic water droplet behavior, self‐cleaning ability, and electrical output performance of the fabrics before and after sequential treatments with O2 plasma for 12 min and CF4 plasma for 4 min are measured. The electrical output performance for all fabric‐based piezoelectric nanogenerators (PENGs) is higher than that for PVDF film‐based PENGs. Furthermore, plasma treatment enhances the electrical output performance of all triboelectric nanogenerators (TENGs), particularly the fabric‐based TENGs. Due to the increased water repellency and self‐cleaning ability conferred by the plasma treatment, all superhydrophobic fabric‐based TENGs exhibit improved stability in electrical output performance when exposed to water or dust particles. In contrast, plasma treatment has little or no effect on the stability of the output performance of the PVDF‐film‐based TENGs. The superhydrophobic PVDF fabric with the highest water repellency and self‐cleaning efficiency exhibits the most stable triboelectric energy‐harvesting performance when exposed to water and dust particles. Because of its micro/nanoscale hierarchical roughness and open‐pore structure, the optimal plasma‐treated PVDF fabric has a reduced contact area with water droplets, rendering this fabric favorable for repelling water droplets and removing particles.

CF4 Plasma-Generated LiF-Li2 C2 Artificial Layers for Dendrite-Free Lithium-Metal Anodes.

Lithium metal anodes have long been considered as “holy grail” in the field of energy storage batteries, but dendrite growth and large volume changes hinder their practical applications. Herein, a facile and eco‐friendly CF4 plasma treatment is employed for the surface modification of Li anodes, and an artificial layer consisting of LiF and Li2C2 is fabricated for the first time. Experimental results and theoretical calculations reveal that the high adsorption energy of LiF and low Li+ diffusion barriers in Li2C2 induce uniform nucleation and planar growth of Li, guaranteeing a stable and dendrite‐free Li structure during the repeated plating/stripping process of cycling. Symmetric cells using CF4 plasma‐treated Li operate stably for more than 6500 h (at 2 mA cm−2 and 1 mAh cm−2) or 950 h (at 1 mA cm−2 and 10 mAh cm−2). When paired with a LiFePO4 cathode, full batteries deliver a high reversible capacity of 136 mAh g−1 (at 1 C) with considerable cycling stability (97.2% capacity retention over 200 cycles) and rate performance (116 mAh g−1 up to 5 C). This powerful application of plasma technology toward novel LiF‐Li2C2 artificial layers provide new routes for constructing environment‐friendly and high‐performance energy storage devices.

Unusual n-type doping of monolayer WSe2 by CF4 plasma treatment

We report unusual n-type doping of monolayer WSe2 by CF4 plasma treatment. Photoluminescence/Raman/x-ray photoelectron spectroscopy measurements implied electron-doping of mechanically-exfoliated WSe2 after CF4 plasma treatment. Such n-type doping is probably due to the use of mild process conditions resulting in Se-deficient monolayer WSe2 with negligible concentration of electronegative F atoms after CF4 plasma treatment. Transistor performance of monolayer WSe2 also confirmed n-type doping by CF4 plasma treatment. These results demonstrate that CF4 plasma treatment under mild process conditions can be an alternative n-type doping method of monolayer WSe2 and other transition metal dichalcogenides for device integration.

Charging Effect by Fluorine-Treatment and Recess Gate for Enhancement-Mode on AlGaN/GaN High Electron Mobility Transistors.

An enhancement-mode AlGaN/GaN metal-insulator-semiconductor high-electron- mobility-transistor was fabricated using a recess gate and CF4 plasma treatment to investigate its reliable applicability to high-power devices and circuits. The fluorinated-gate device showed hysteresis during the DC current-voltage measurement, and the polarity and magnitude of hysteresis depend on the drain voltage. The hysteresis phenomenon is due to the electron trapping at the Al2O3/AlGaN interface and charging times longer than milliseconds were obtained by pulse I-V measurement. In addition, the subthreshold slope of the fluorinated-gate device was increased after the positive gate bias stress because of the two-dimensional electron gas reduction by ionized fluorine. Our systematic observation revealed that the effect of fluorine ions should be considered for the design of AlGaN/GaN power circuits.

Effects of CF4 Plasma Treatment on Indium Gallium Oxide and Ti-doped Indium Gallium Oxide Sensing Membranes in Electrolyte–Insulator–Semiconductors

Electrolyte–insulator–semiconductor (EIS) sensors, used in applications such as pH sensing and sodium ion sensing, are the most basic type of ion-sensitive field-effect transistor (ISFET) membranes. Currently, some of the most popular techniques for synthesizing such sensors are chemical vapor deposition, reactive sputtering and sol-gel deposition. However, there are certain limitations on such techniques, such as reliability concerns and isolation problems. In this research, a novel design of an EIS membrane consisting of an optical material of indium gallium oxide (IGO) was demonstrated. Compared with conventional treatment such as annealing, Ti doping and CF4 plasma treatment were incorporated in the fabrication of the film. Because of the effective treatment of doping and plasma treatment, the defects were mitigated and the membrane capacitance was boosted. Therefore, the pH sensitivity can be increased up to 60.8 mV/pH. In addition, the hysteresis voltage can be improved down to 2.1 mV, and the drift voltage can be suppressed to as low as 0.23 mV/h. IGO-based membranes are promising for future high-sensitivity and -stability devices integrated with optical applications.

Characterization and Analysis of Metal Adhesion to Parylene Polymer Substrate Using Scotch Tape Test for Peripheral Neural Probe.

This paper presents measurement and FEM (Finite Element Method) analysis of metal adhesion force to a parylene substrate for implantable neural probe. A test device composed of 300 nm-thick gold and 30 nm-thick titanium metal electrodes on top of parylene substrate was prepared. The metal electrodes suffer from delamination during wet metal patterning process; thus, CF4 plasma treatment was applied to the parylene substrate before metal deposition. The two thin film metal layers were deposited by e-beam evaporation process. Metal electrodes had 200 μm in width, 300 μm spacing between the metal lines, and 5 mm length as the neural probe. Adhesion force of the metal lines to parylene substrate was measured with scotch tape test. Angle between the scotch tape and the test device substrate changed from 60° to 90° during characterization. Force exerted the scotch tape was recorded as the function of displacement of the scotch tape. It was found that a peak was created in measured force-displacement curve due to metal delamination. Metal adhesion was estimated 1.3 J/m2 by referring to the force peak and metal width at the force-displacement curve. Besides, the scotch tape test was simulated to comprehend delamination behavior of the test through FEM modeling.

Enhanced piezoelectric tactile sensing behaviors of high-density and low-damage CF4-plasma-treated IGZO thin-film transistors coated by P(VDF-TrFE) copolymers

Piezoelectric pressure sensing behaviors of high-density and low-damage CF4-plasma-treated indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) coated by poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) films have been investigated. The CF4 plasma treatment was performed on the IGZO channel by using an inductively coupled plasma (ICP) system with a quartz filter. Prior to the fabrication of devices, X-ray diffractometer (XRD) and atomic force microscopy (AFM) were applied to identify the enhancement in the crystallinity of P(VDF-TrFE) films on the plasma-fluorinated IGZO films. With the analyses of X-ray photoelectron spectroscopy (XPS), it is proved that the fluorine radicals reacted with the metal-oxygen bonds will increase the oxygen vacancies in IGZO films, contributing to an enhancement in field effect mobility (μFE) and drain current (IDS) of IGZO TFTs. Furthermore, the fluorine atoms diffused from the IGZO channel into the bottom SiO2 layer were confirmed by secondary ion-mass spectroscopy (SIMS), reducing the interfacial and oxide charges of the devices for a negative shift in threshold voltage (Vt). Under a 0.5-kg applied force press/release cyclic test, a 4.8-fold increase in drain current response of 1-min CF4-plasma-treated piezoelectric pressure sensors was optimized, because of the enhanced electrical behaviors of IGZO TFTs and an increase in aligned dipole moments of P(VDF-TrFE) copolymers. The promising results make the piezoelectric pressure sensors with high-density and low-damage CF4-plasma-treated IGZO TFTs coated by P(VDF-TrFE) copolymer suitable for future high-performance tactile sensing applications.