Application of Self-Assembled Monolayers to InGaZnO Thin Film Transistors

Investigations on the application of self-assembled monolayers (SAM) to indium gallium zinc oxide (IGZO) thin film transistors (TFT) for fabrication and channel modification are presented. The back channel of IGZO thin film transistors can be modified by the absorption of self-assembled monolayers. The electrical properties of the IGZO exposed back channel are sensitive to surface chemistries and can be tailored using SAMs. Chemistry at the back channel interface alters device performance. The back channel surface sensitivities can be used in applications for chemical sensing TFTs. IGZO TFTs with and without octadecyl phosphonic acid applied to the back channel with varied channel thicknesses (10-50 nm) were examined. TFT parameters, such as, turn-on voltage, hysteresis, mobility, subthreshold swing, and current on/off ratio were evaluated by current-voltage electrical measurements. The use of electrohydrodynamic ink jet (EHDP) printing as non-contact method for patterning etch resists with sub-10 μm features was demonstrated for fabrication of IGZO TFTs. EHDP uses an electric field to generate ink droplets that can be smaller than the nozzle diameter. EHDP was used for depositing a self-assembled monolayer, n-hexyl phosphonic acid (HPA), and photoresist, SU8, as etch resists for patterning the IGZO TFT channel. Drop on demand printing is accomplished by overlapping of discrete droplets to form the desired feature. The optimal ink formulations and EHDP parameters were determined for each ink. Parameters were optimized for producing the smallest, uniform printed features. Bottom gate IGZO TFTs were fabricated by plasma sputtering IGZO onto a SiO₂/Si substrate. The IGZO TFT channels were patterned by printing HPA or SU8 ink as the etch resist, and using HCl as the etch solution. Indium tin oxide source and drain were deposited over the patterned channel using plasma sputtering. The electrical performance of IGZO TFTs patterned using HPA and SU8 were compared and evaluated using I-V electrical measurements. Drop on demand printing offers a high-speed, low cost route to TFT fabrication and manufacturing. The long narrow channels produced have applications for TFT sensor technologies. EHDP was shown to be capable of printing etch resists for the patterning and fabrication of IGZO TFTs on the scales relevant for digital displays

Role of Self-Assembled Monolayers on Improved Electrical Stability of Amorphous In-Ga-Zn-O Thin-Film Transistors

Self-assembled monolayers (SAMs) have been used to improve both the positive and negative bias-stress stability of amorphous indium gallium zinc oxide (IGZO) bottom gate thin film transistors (TFTs). N-hexylphosphonic acid (HPA) and fluorinated hexylphosphonic acid (FPA) SAMs adsorbed on IGZO back channel surfaces were shown to significantly reduce bias-stress turn-on voltage shifts compared to IGZO back channel surfaces with no SAMs. FPA was found to have a lower surface energy and lower packing density than HPA, as well as lower bias-stress turn-on voltage shifts. The improved stability of IGZO TFTs with SAMs can be primarily attributed to a reduction in molecular adsorption of contaminants on the IGZO back channel surface and minimal trapping states present with phosphonic acid binding to the IGZO surface.Keywords: Layer deposition, Tin oxid

Fabrication of a Flexible Amperometric Glucose Sensor Using Additive Processes

This study details the use of printing and other additive processes to fabricate a novel amperometric glucose sensor. The sensor was fabricated using a Au coated 12.7 μm thick polyimide substrate as a starting material, where micro-contact printing, electrochemical plating, chloridization, electrohydrodynamic jet (e-jet) printing, and spin coating were used to pattern, deposit, chloridize, print, and coat functional materials, respectively. We have found that e-jet printing was effective for the deposition and patterning of glucose oxidase inks with lateral feature sizes between ∼5 to 1000 μm in width, and that the glucose oxidase was still active after printing. The thickness of the permselective layer was optimized to obtain a linear response for glucose concentrations up to 32 mM and no response to acetaminophen, a common interfering compound, was observed. The use of such thin polyimide substrates allow wrapping of the sensors around catheters with high radius of curvature ∼250 μm, where additive and microfabrication methods may allow significant cost reductions

Glucose Sensing Using Functionalized Amorphous In–Ga–Zn–O Field-Effect Transistors

Recent advances in glucose sensing have focused on the integration of sensors into contact lenses to allow noninvasive continuous glucose monitoring. Current technologies focus primarily on enzyme-based electrochemical sensing which requires multiple nontransparent electrodes to be integrated. Herein, we leverage amorphous indium gallium zinc oxide (IGZO) field-effect transistors (FETs), which have found use in a wide range of display applications and can be made fully transparent. Bottom-gated IGZO-FETs can have significant changes in electrical characteristics when the back-channel is exposed to different environments. We have functionalized the back-channel of IGZO-FETs with aminosilane groups that are cross-linked to glucose oxidase and have demonstrated that these devices have high sensitivity to changes in glucose concentrations. Glucose sensing occurs through the decrease in pH during glucose oxidation, which modulates the positive charge of the aminosilane groups attached to the IGZO surface. The change in charge affects the number of acceptor-like surface states which can deplete electron density in the n-type IGZO semiconductor. Increasing glucose concentrations leads to an increase in acceptor states and a decrease in drain-source conductance due to a positive shift in the turn-on voltage. The functionalized IGZO-FET devices are effective in minimizing detection of interfering compounds including acetaminophen and ascorbic acid. These studies suggest that IGZO FETs can be effective for monitoring glucose concentrations in a variety of environments, including those where fully transparent sensing elements may be of interest

DuXiaosongChemBioEnvEngFabricationFlexible.pdf

This study details the use of printing and other additive processes to fabricate a novel amperometric glucose sensor. The sensor was fabricated using a Au coated 12.7 μm thick polyimide substrate as a starting material, where micro-contact printing, electrochemical plating, chloridization, electrohydrodynamic jet (e-jet) printing, and spin coating were used to pattern, deposit, chloridize, print, and coat functional materials, respectively. We have found that e-jet printing was effective for the deposition and patterning of glucose oxidase inks with lateral feature sizes between ∼5 to 1000 μm in width, and that the glucose oxidase was still active after printing. The thickness of the permselective layer was optimized to obtain a linear response for glucose concentrations up to 32 mM and no response to acetaminophen, a common interfering compound, was observed. The use of such thin polyimide substrates allow wrapping of the sensors around catheters with high radius of curvature ∼250 μm, where additive and microfabrication methods may allow significant cost reductions

DuXiaosongChemBioEnvEngFabricationFlexible.pdf

This study details the use of printing and other additive processes to fabricate a novel amperometric glucose sensor. The sensor was fabricated using a Au coated 12.7 μm thick polyimide substrate as a starting material, where micro-contact printing, electrochemical plating, chloridization, electrohydrodynamic jet (e-jet) printing, and spin coating were used to pattern, deposit, chloridize, print, and coat functional materials, respectively. We have found that e-jet printing was effective for the deposition and patterning of glucose oxidase inks with lateral feature sizes between ∼5 to 1000 μm in width, and that the glucose oxidase was still active after printing. The thickness of the permselective layer was optimized to obtain a linear response for glucose concentrations up to 32 mM and no response to acetaminophen, a common interfering compound, was observed. The use of such thin polyimide substrates allow wrapping of the sensors around catheters with high radius of curvature ∼250 μm, where additive and microfabrication methods may allow significant cost reductions

Abstracts of the 3rd Annual Graduate Entry Research in Medicine Conference

This book contains the abstracts of the papers presented at The 3rd Annual Graduate Entry Research in Medicine Conference (GERMCON 2020) Organized by Warwick Medical School, University of Warwick in collaboration with Swansea University Medical School, Swansea University, Wales, UK held on 12–18 October 2020. This was especially important for Graduate Entry Medical (GEM) students, who have less opportunity and time to engage in research due to their accelerated medical degree. Conference Title: 3rd Annual Graduate Entry Research in Medicine ConferenceConference Acronym: GERMCON 2020Conference Date: 12–18 October 2020Conference Location: Online (Virtual Mode)Conference Organizer: Warwick Medical School, University of Warwick, UKCo-organizer: Swansea University Medical School, Swansea University, Wales, UK Other Abstract Book of GERMCON: Abstracts of the 4th Annual Graduate Entry Research in Medicine Conferenc