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Inverted-structure perovskite devices with PEDOT and PEDOT/CuI as hole transport layers (HTLs) were prepared on Glass/ITO substrates. Surface morphology observation of the CuI revealed that the CuI grew on PEDOT in island mode. A concentration of 20 mg/ml was necessary for continuous CuI formation on the PEDOT. Optimization of the annealing time and the concentration of CuI precursor solution led to a PCE of 16.5% for a device with PEDOT/CuI as HTL, which was slightly higher than that (15%) with PEDOT as HTL. The slight enhancement of PCE was due to the faster hole transport efficiency and improved light-harvesting in the visible light region. Additionally, the photostability of the devices was greatly enhanced by the insertion of the CuI layer. Analysis indicated that the insertion of the CuI decreased the transmittance of light with wavelengths within 320–410 nm, which was the main reason for the enhanced photostability.

In this study, we reported a low-temperature, one-step solution process to fabricate perovskite solar cells using dehydrated lead acetate as the lead source. These perovskite films were aged at 200 s before thermal annealing at 90 °C for 5 min. Uniform perovskite films with lesser pinholes were obtained by this technique. The inverted planar (n-i-p) perovskite solar cell device resulted in a power conversion efficiency of 13%. A substantial finding was that the devices demonstrated high reproducibility. We also investigated the effect of annealing temperature on the optical and structural properties of the films and on the photovoltaic performances of the fabricated solar cell devices. For the aforementioned, a low-temperature, one-step solution process, the optimal temperature was achieved at 90 °C.

The existence of the Schottky barriers at the top and bottom electrodes of the ferroelectric thin film sandwich structure makes it difficult to separate and collect electron-hole pairs, thus limiting the enhancement of the photocurrent. In this paper, Pb(Zr,Ti)O3 (PZT) and composite structure of PZT/CuO films are prepared by a sol-gel method and their photovoltaic properties have been investigated. It is found that the PZT/CuO films show a short circuit photocurrent density (JSC) enhanced by nearly 6 times and power conversion efficiency (PCE) increased by six-fold when compared to those of the PZT film. The increase of photovoltaic response is due to the internal electric field of PZT/CuO p–n junction, which plays an important role in driving the photo-generated carriers. The Ohmic contact between the interfaces of LNO/PZT and CuO/Pt also reduce the resistance of the transportation of photogenerated carriers. Furthermore, the JSC of PZT/CuO film are observed to be 0.03 and 0.013 mA/cm2 after upward poling and downward poling, respectively, indicating that the photocurrent can be modulated by the direction of the polarization electric field. The photovoltaic effect of composite films and its potential mechanism are also explored. This work provides an efficient approach to develop ferroelectric film based on photovoltaic devices.

Transparent composite electrodes (TCE), TiO2/Ag/TiO2 (TAgT), have been demonstrated as a promising alternative of indium tin oxide (ITO) in organic solar cell application. TiO2/Ag/TiO2 have been incorporated into bulk heterojunction organic solar cells (OSCs) to replace ITO as the anode. Two different hole transfer layers (HTL), poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and MoO3, are compared in terms of their compatibility with the TiO2/Ag/TiO2 anode. The MoO3 layer has been shown to be a beneficial HTL for TiO2/Ag/TiO2 based OSC. However, the wettability of MoO3 for polymer blend is not as good as PEDOT:PSS, and results in a relatively thin active layer in OSCs. On the other hand, ITO based OSCs using PEDOT:PSS and MoO3 as the HTL are fabricated as control samples to compare the performance of TAgT and ITO anodes. Results of the investigation shows that the superior electrical property of TAgT anodes contributes to the effective collection of photo-carriers and its lower optical transmittance barely degrades the light absorption in OSCs. In a few words, the higher Haacke figure of merit of TAgT enables better performance of OSCs with MoO3 HTL, in comparison with ITO based OSC.

A novel ultraviolet photochemical method was used to prepare TiO2 resistive-switching films. Amorphous TiO2 films were formed on flexible indium-tin oxide (ITO) coated polyethylene terephthalate (PET) substrates by deep ultraviolet irradiation at 150 °C. A Pt/TiO2/ITO/PET device was then fabricated to investigate bipolar resistive switching of the films for potential application in non-volatile memories. The ratio of on-state to off-state currents was measured, and a good value of 1000 was obtained. The retention and switch-cycling characteristics of the device were investigated for different bending radii. The resistive switching behavior of the flexible device remained stable after 600 cycles of electrical switching and 1000 cycles of bending.

As a promising indium-free electrode, transparent composite electrode (TCE) TiO 2 /Ag/TiO 2 is an attractive alternative to indium tin oxide (ITO). The multilayer structure of TiO 2 /Ag/TiO 2 is deposited on glass substrate by room-temperature sputtering. The effects of deposition rate, thickness of Ag and TiO 2 layers on the electrical and optical properties of this TCE are presented. Results show that the Ag films tend to have fewer voids to form, if the Ag deposition rate is sufficiently high. The presence of fewer voids in the Ag layer results in higher transmittance and lower sheet resistance of the corresponding TiO 2 /Ag/TiO 2 structure. In order to increase the solar input to the P 3 HT:PC 61 BM organic solar cell, the layer thicknesses of TiO 2 /Ag/TiO 2 electrodes are theoretically and then experimentally optimized, such that its optical transmittances are maximized across the wavelength range where the light absorption of P 3 HT:PC 61 BM is highest. In this study, the device-specific Haacke figure of merit (FOM) of the TiO 2 /Ag/TiO 2 electrode is optimal with the use of 42 nm TiO 2 layers and 10 nm Ag layer. This optimal Haacke FOM is two times higher than that of ITO electrodes. The conventional bulk heterojunction organic solar cell (OSC) fabricated on optimized TiO 2 /Ag/TiO 2 electrode shows high power conversion efficiency (PCE), almost 100% higher than PCE of OSC fabricated on ITO. Our finding indicates that TiO 2 /Ag/TiO 2 electrode can be specifically tailored to particular applications. It can be implemented in organic solar cell and has considerable potential to replace ITO in solar cell applications.

Silver-chalcogenide glass flexible sensors were tested to study the impact of physical design parameters on the performance characteristics of the sensors in response to ionizing radiation. Results show that by changing lateral spacing between adjacent electrodes, the limit of detection and dynamic range can be regulated. Likewise, by changing the diameter of the electrodes, the sensor high and low resistance states can be adjusted to a desired range. In contrast, the influence of the electrode diameter on the sensor performance characteristics was found to have less of an impact on sensor performance. Mechanisms for ion transport and reactions are investigated using TCAD simulations in which the standard statistics and transport equations for free carriers are simultaneously solved. The simulation results are qualitatively in a good agreement with experimental data.

Electrochromic films have been used as a non-emissive material for display applications. Such materials have already been integrated in antiglare rearview mirrors for passenger vehicles as well as smart windows intended for energy savings for buildings. However, most electrochromic materials are deposited on rigid substrates, which prevent its use in flexible and stretchable electronic applications, where low temperature deposition techniques are desired. Additionally, electrochormics require an external power source to drive the underlying reduction/oxidation reaction. In this work, electrochromic materials inkjet-printed onto flexible and stretchable substrates have been explored. These devices are "self-powered" by organic solar cells also fabricated on flexible and stretchable substrate such as PDMS and PET. A set of inks based on a combination of synthesized and commercially obtained WO_3 nanoparticles, W-TiO_2 and TiO_2 nanoparticles were evaluated. The microstructure of the nanoparticles used in this study were examined under scanning electron microscopy for examining nanoparticle morphology, x-ray diffraction for chemical and structural characterization, and dynamic light scattering for particle size determination. Electrochromic layers were then ink-jet printed on flexible and stretchable PDMS substrates, using synthesized Ag nanowires as conductive, yet highly transparent electrodes. The stretchable printed electrochromic devices under various stress conditions and electrochromic performances were evaluated and demonstrated clear switching behavior under external bias, with 7 second coloration time, 8 second bleaching time, and 0.36-0.75 optical modulation at ?=525 nm. Cyclic voltammetry and galvanostatic charge/discharge measurements demonstrated high areal capacitance, with limited stability upon cycled operation. The electrochromic devices were then integrated in an Internet of Things (IoT)-enabled switching configuration, self-powered by PCDTBT:PC_70BM organic photovoltaics. The bulk heterojunction devices were evaluated with varying hole-transport layers and substrates, and exhibited the strongest performance of PCE? 3%, V_oc=0.9V and J_sc ? 10-15 mA/cm^2. The described self-powered, IoT-enabled, ink-jet printed electrochromic devices, fabricated on flexible substrates, are demonstrative of potential applications for wearable electronics.

A low temperature sol-gel process was used to fabricate zinc-oxide and yttrium-doped zinc oxide layers. These zinc-oxide and yttrium-doped ZnO films were used as electron transport layers in conjunction with P3HT and PC16BM type solar cells. It was demonstrated that annealing and doping of electron transport layer influenced the overall organic solar cells performance. Anneals of ~ 150?C provided the highest device performance. Compared to the undoped zinc oxide, the device with yttrium doped zinc oxide layers showed improved efficiency by about 30%. Furthermore an equivalent circuit was proposed to understand the connection between the electrical and optical characteristics of the device. Comparisons between the simulated and experimental current-voltage(I-V) curves displayed only a 1.2% variation between the curves. Clearly, our experimental and simulated studies provide new insight on the equivalent circuit models for inverted organic solar cells and further improvement on photovoltaic efficiency.

Carrier recombination lifetime is a key semiconductor parameter that not only has a major role in how a variety of solid-state devices operate, but one that can also be used as a process cleanliness monitoring tool. Lifetime measurement on epitaxial wafers, where the epilayer thickness is smaller than the minority carrier’s diffusion length, has always been a challenging task. Although the pulsed MOS capacitor has been shown to be an eminently suitable technique for measuring the generation lifetime ( $\tau _{g})$ on these wafers, measuring the recombination lifetime ( $\tau _{r})$ yet has remained complicated and difficult to implement. In this paper, a new technique for accurate measurement of $\tau _{r}$ will be presented. Lifetime will be extracted from the capacitance transient ( $C$ – $t$ ) of an inverted MOS device while being excited by an optical pulse. In addition to its easy implementation, the recombination lifetime extracted this way is least affected by Si/SiO2 surface and epi/substrate interface effects when compared with older techniques such as the photoconductance decay. TCAD simulations and experimental results will be presented to demonstrate the promising application of the optically excited MOS to the characterization of p/p+ silicon epitaxial layers.

Multilayer structures of TiO2/Au/TiO2 have been deposited onto flexible substrates by room temperature sputtering to develop indium-free transparent composite electrodes (TCEs). The effect of Au thicknesses on optical, electrical properties and the mechanism of conduction have been discussed. The electrical conductivity of the TCEs is solely contributed by the middle metal layer. The critical thickness (t c) of the Au mid-layer to form a continuous conducting layer is 10 nm, and the multilayer has been optimized to obtain a sheet resistance of 12.2 Ω/sq and an average optical transmittance of 86% at 590 nm. The Haacke figure of merit (FOM) for t c has one of the highest FOM with 18 × 10−3 Ω−1. The samples were annealed in various environments for 24 h up to 150°C.

The interest in indium-free transparent composite electrode (TCE), a thin metal layer embedded between two transparent metal oxide (TMO) layers resulting in TMO/metal/TMO composite structure, has grown recently with the advent of their high figures of merit and its potential application in photovoltaic applications. However, most of the work to date has focused on experimentally producing the best optically transmitting TCE. To better design TCEs and minimize experimental work, it would be useful to develop a model that predicts the optical transmission. In the current work, the transfer-matrix method is employed to calculate the transmittance spectrum of TCE. To validate this approach, the transmittance spectra of TiO2/Au/TiO2 and TiO2/Ag/TiO2 multilayer thin-film TCEs are calculated with use of extracted material parameters. The calculated transmittance spectrum of TiO2/Au/TiO2 matches the measured spectrum quite well. However, the calcualted transmittance of TiO2/Ag/TiO2 is higher than its measured transmittance. The presence of voids in the Ag film is probably responsible for the decreased transmittance of the TiO2/Ag/TiO2 sample, and the continuous Au film in TiO2/Au/TiO2 ensures a good agreement between transmittance prediction and measurement. Our approach is a reliable tool to predict the optical transmittance of TCE with continuous films, and it can efficiently expedite the selection from numerous possible combinations of transparent metal oxides and metals when developing TCEs for future photovoltaic applications. It can also serve as a convenient method to assess the continuity of embedded metal layer.

aSchool for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287, USA bCHD-Fab, Freescale Semiconductor Inc., Tempe, Arizona 85284, USA cKorea Institute of Science and Technology, Seoul, South Korea dSchool of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, USA eDepartment of Chemical and Materials Engineering, University of Nevada, Reno, Nevada 89557, USA

Zinc-oxide and yttrium-doped ZnO films were fabricated by a sol–gel processing technique and were incorporated as an electron transport layer in inverted organic solar cells (with an active layer comprising a blend of P3HT and PC61BM). First, the annealing conditions for the pure sol–gel ZnO layers were optimized. An interesting observation was that the annealing temperature of the ZnO layer significantly influenced the overall organic solar cells performance. Annealing the ZnO film at temperatures of ∼150 °C provided the highest device performance. The physical and surface properties of these ZnO films were examined by X-ray diffraction, atomic force microscopy and UV-vis transmittance measurements. Utilizing the optimized annealing conditions, we further fabricated high-efficiency organic solar cells by doping yttrium in the zinc-oxide (YZO) electron transport layers. The efficiency of YZO based devices was improved by 30% when compared to that of the undoped zinc oxide based devices.

In this paper, previous work on chalcogenide-glass (ChG)-based radiation sensors is extended to include the effects of mechanical strain and temperature stress on sensors formed on a flexible polymer substrate. We demonstrate the feasibility of producing inexpensive flexible radiation sensors, which utilize radiation-induced migration of ${\rm Ag}^{+}$ ions in germanium selenide ( ${\rm Ge}_{20}{\rm Se}_{80}$ ) films to produce a decrease in resistance of several orders of magnitude between surface electrodes. This change in resistance can be related to total ionizing dose to give an instantaneous readout of radiation exposure. The ChG films are inherently flexible and this, along with an extremely simple device fabrication process at or near room temperature, allows inexpensive sensor structures to be fabricated on lightweight pliable polymeric substrates such as polyethylene napthalate (PEN). Test samples were irradiated with ionizing radiation (UV light and $^{60}$ Cobalt gamma rays). Irradiated samples were subjected to both tensile and compressive stress, and elevated operating temperatures. Stress and exposure to increased ambient temperature had little effect on device resistance. Analysis of the experimental data is supported by the results of COMSOL simulations that model radiation-induced lateral Ag diffusion in ChG.

We demonstrate the power conversion efficiency of bulk heterojunction organic solar cells can be enhanced by introducing Ag nanoparticles into organic exciton blocking layer. The Ag nanoparticles were incorporated into the exciton blocking layer by thermal evaporation. Compared with the conventional cathode contact materials such as Al, LiF/Al, devices with Ag nanoparticles incorporated in the exciton blocking layer showed lower series resistances and higher fill factors, leading to a 3.2% power conversion efficiency with a 60 nm active layer; whereas, the conventional devices have only 2.0–2.3% power conversion efficiency. Localized surface plasmon resonances by the Ag nanoparticles and their contribution to photocurrent were also discussed by simulating optical absorptions using a FDTD (finite-difference-time-domain) method.

For the first time it is reported that nitrogen-doped titanium oxide with light annealing can improve the device performance by 300% when acting as an interfacial layer between CdSe quantum dot/poly-3-hexylthiophene and the cathode in the photovoltaic devices. Substitutional N doping with a concentration of 1.2 at.% was found by X-ray photoelectron spectroscopy which was responsible for 0.1 eV band gap reduction of TiOx. Photoluminescence and the external quantum efficiency spectrum confirmed the enhanced charge collection and association rate after light annealing. Three-dimensional atomic force microscopy results agreed with the series resistance measurements, confirming that a good contact was achieved. The topography study also indicated that the active layer morphology changed upon light annealing. Improved stability and longer lifetime were also found with TiOxNy capped devices, which were optimized with light annealing. TiOx capped devices were also evaluated for comparison in this study.

Yttrium doped zinc oxide (ZnO) nanowires prepared on seedless indium tin oxide (ITO) substrates were used for nanostructured bulk heterojunction organic solar cells (OSCs). Without patterning by a mask, the optimized areal density of ZnO nanowires decreased the reflection of incident light impinging upon the substrate by more than 50%, resulting in better incident-photon to current efficiencies (IPCEs) than for solar cells without ZnO nanostructures. OSC decorated with yttrium doped ZnO nanostructures showed an increase in current density from 8.9 mA/cm2 to 9.9 mA/cm2 resulting in 15% better device performance than a planar bulk heterojunction OSC. It was found that the antireflective effect due to ZnO nanowires was maximized with an areal density of 50 nanowires per 100 μm2. The areal density was optimized by incorporation of 0.02 mM yttrium chloride into the growth solution during nanostructure formation. In addition, OSC that incorporated the optimized areal density and length of ZnO nanostructures showed a 25% improved power conversion efficiency of 2.5% compared to OSC prepared on an ITO substrate without the ZnO nanostructures. Our results indicate that growth of density-controlled ZnO nanowire arrays on seedless ITO substrates using yttrium dopant is simple, low cost, and easily controllable method that enables low temperature fabrication, without patterning, of antireflective structures for significantly enhanced efficiency bulk heterojunction OSCs.

We report on the electrical and optical properties of ZnO/Ag/MoO 3 (ZAM) multilayer electrodes deposited directly on glass substrates by a combination of radio frequency (RF) and direct current (DC) sputtering for bulk-heterojunction organic solar cells (OSCs). Compared to indium tin oxide (ITO) electrodes showing 20 Ω/sq, the transparent composite electrodes (TCE) in this study exhibited very low sheet resistance of 5 Ω/sq without post annealing. In addition, as a hole transport layer, the MoO 3 performed with a higher fill factor than PEDOT:PSS due to lower series resistance, resulting in a power conversion efficiency of 2.3%, V oc of 0.59 V, and J sc of 9 mA/cm 2 . The power conversion efficiency of the OSC with the ZAM electrode is lower than that of organic solar cells on ITO which has 3.3% efficiency, due to lower transmittance after MoO 3 layer deposition. However, our results do support the possibility of using MoO 3 as both Ag protecting and hole transport layers for indium-less and PEDOT:PSS-less bulk-heterojunction OSCs.

We develop a modified pulsed MOS technique for measuring generation lifetime in ultraclean and thin p/p+ epitaxial layers, which can be used to detect metallic impurities with densities as low as 1010cm-3. The widely used classic version is shown to be unable to effectively detect such low impurity densities because of the domination of surface generation; whereas, recombination lifetime measurement techniques have serious limitations for layers that have smaller thicknesses than the minority carrier diffusion length.

This study reports the operational instability and failure causing defect mechanisms of indium gallium zinc oxides based thin film transistors (TFTs) under practical, combined bias and illumination stress conditions. The effect of the illumination stress with light source of different wavelengths (410 nm, 467 nm, 532 nm, and 632 nm) has been explained. Wavelengths shorter than green light (532 nm) demonstrate creation of ionized vacancies and subsequent generation of excess carriers that alter TFT functions. Recovery evaluations performed upon removal of combinatory stresses exhibits incomplete recovery due to incapacity in regenerating neutral oxygen vacancies. The Ion/Ioff values show an increase by an order of magnitude when compared to previous studies where the Ion/Ioff is reduced. This can be contributed to the reduced defect and vacancy densities due to the effective post anneal process.

Thin films of amorphous indium gallium zinc oxide with high transmittance were deposited at room temperature onto flexible polymer substrates. Postdeposition anneals were performed at low temperatures in different ambients to obtain films with one of the highest transmittance and mobility values reported in the literature. As-deposited and postanneal films were characterized for electrical and optical properties. Oxygen anneal degraded the electrical performance of the films, which was recovered by succeeding vacuum anneals. A surface scattering model is proposed to determine the relation between mobility and carrier concentrations at low values of carrier concentrations. This model takes into account electronic scattering as a result of grain structure and morphology.

We have investigated the optical properties of sputter-deposited silver-copper alloy thin films on silicon substrates at room temperature. We found that alloying copper with silver can significantly improve the metal’s surface morphology, keeping its infrared reflectivity same as that of pure silver film. However at the same time, it worsens in the blue parts of the spectrum. The reflection in Ag-Cu thin films is interpreted in terms of a simple model describing its trend due to alloying. The experimental results and the speculations reveal a prospect for the improvement and optimization of solar reflectors.

Community-based participatory research (CBPR) is becoming one of the dominant approaches for bringing evidence- and consensus-based cancer prevention and control practices to medically underserved communities. There are many examples of how CBPR has been useful for generating culturally specific solutions for different health issues that affect African-Americans. However, few examples exist in the literature on how the CBPR approach can be applied to address prostate cancer. This paper describes a collaborative process for linking inner-city, African-American men to free prostate cancer education, physician counseling, and screening opportunities (prostate-specific antigen (PSA) testing and digital rectal examination (DRE)). The site of this community-based participatory project was the city of Buffalo, located in Erie County, New York. The collaborative, community-academic process that is described includes the following: (1) planning and conducting a community needs assessment to contextualize local prostate cancer issues, (2) organizing town and gown event planning, and (3) manipulating aspects of the built environment to build an infrastructure within the community to address disparities in screening opportunities. This paper concludes with a description of lessons learned that can help others develop and implement similar activities in other communities.

This paper investigates the variation of electrical characteristic of indium gallium zinc oxide (IGZO) thin film transistors (TFTs) under gate bias stress. The devices are subjected to positive and negative gate bias stress for prolonged time periods. The effect of bias stress time and polarity on the transistor current equation is investigated and the underlying effects responsible for these variations are determined. Negative gate stress produces a positive shift in the threshold voltage. This can be noted as a variation from prior studies. Due to variation of power factor (n) from two, the integral method is implemented to extract threshold voltage (vt) and power factor (n). Effective, mobility (ueff), drain to source resistance (RDS) and constant k' is also extracted from the device characteristics. The unstressed value of n is deter-mined to be 2.5. The power factor increases with gate bias stress time. The distribution of states in the conduction band is revealed by the variation in power factor.

The change in electrical characteristics of a-Si:H thin-film transistors (TFTs) was determined in the presence of electrical gate bias stress, gamma radiation, and both simultaneously, simulating the harsh environment of space. Multiple TFTs were tested under each condition, and the current-voltage characteristics were measured. The results show the gate bias stress increasing the threshold voltage (VT) with power law time dependence while the gamma irradiation decreases threshold voltage for all working transistors. When both the irradiation and gate bias stress were applied simultaneously, the VT initially increased with electrical stress and then decreased as the gamma radiation dominated. Changes in effective mobility were also extracted and detailed analysis of the current-voltage characteristics indicated that the gamma radiation creates interface traps and electron-hole pairs whereas the gate stress produces defect states in the amorphous silicon.

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) are widely used as controlling devices for picture pixels in liquid crystal displays. In addition to flat panel display applications, a significant research effort focuses on the extension of this technology to circuitry on flexible substrates to build flexible sensor systems. This study investigates the effect of anneal time on the performance of the a-Si:H TFTs on Polyethylene naphthalate (PEN). Off-current is reduced by two orders of magnitude for 48-hours annealed TFT, and the sub-threshold slope become steeper with longer annealing. For positive gate-bias-stress, ΔVt values are positive and exhibit a power-law time dependence (PLTD). The 48-hour annealed TFTs, however, display a turnaround phenomenon (TP) at longer stress times. For negative gate-bias-stress, TFTs annealed for ≥ 24 hours possess a smaller positive ΔVt. They do not follow a PLTD and the TP is observed at longer stress times. The observed ΔVt is explained in terms of the shift in the electron and hole transfer characteristics.

A three-electrode electrochemical biosensor has been developed using printed circuit boards for detecting bacterial contamination. This low-cost, small-size device consists of thin-film gold electrodes and is fabricated using photo-lithography paired with electro-deposition. Pathogen presence is deduced by detection of change in electrical impedance caused by binding of the pathogen to bio-receptors coated on the sensor surface. The biosensor has a total area of 3.2 cm and requires only 100 L of test sample for detection. The sensor geometry has been optimized using techniques from Design of Experiments, and the device can be operated using a small ac excitation potential of magnitude 5 mV. The sensor is tested on the common food-borne pathogen Salmonella typhimurium and is able detect bacterial concentrations of the order of 500 CFU/mL within 6 min. In this paper, the design and fabrication of the biosensor is detailed along with the experiments that validate its performance.

Reverse recovery behavior is a useful tool for monitoring lifetime variations in the body diode of power MOSFETs. However, correct interpretation of the laterally diffused MOSFET (LDMOS) reverse recovery is challenging and requires special attention. This is due to the fact that the stored charges in the LDMOS drift region can flow from two different directions with each having different lifetime values. By studying the effects of diode reverse bias and gate voltage on the current flow direction during the reverse recovery, we present a simple approach to extract meaningful lifetime values, which can be used to determine material quality at different locations in the drift region of the LDMOS devices.

In this paper, the optoelectronic properties and morphological features of indium-free ZnO/Ag/MoOx electrodes deposited by in situ combination of RF and DC sputtering at room temperature for low-cost organic photovoltaics has been discussed. The transparent composite electrode (ZnO/Ag/MoOx) was optimized by inspecting the formation of a continuous Ag thin film on top of the ZnO layer. It was found that a 9 nm thick Ag film had the best Haacke figure of merit. Organic solar cells on these composite electrodes revealed good optical and electrical properties, making them a promising alternative indium-free and PEDOT:PSS-free organic solar cells.

Carrier recombination lifetime measurements have always been a challenging task when performed on epitaxial layers. This is due to the fact that most techniques determine the lifetime value by measuring the minority carriers' diffusion length. We will present a new method for measuring the lifetime parameter using light excitation on a MOS-capacitor that is biased into heavy inversion. The annihilation of the optically generated carriers under the shield of an existing depletion region simplifies the mathematical analysis. We show that our proposed approach, corroborated by experimental results, is capable of monitoring lifetime variations due to the presence of metallic impurities as low as 10 10 cm -3 .

We have investigated the effect of anneal time on the performance and temperature-dependent stability of low-temperature-fabricated (180°C) hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) on flexible substrates. For TFTs annealed for 48 h, the subthreshold slope and off-current were reduced by a factor of ~3 and by two orders of magnitude, respectively, when compared to unannealed TFTs. Furthermore, longer annealed TFTs showed a significant improvement in their stability when compared to unannealed TFTs. The lifetime values for the 48- and 96-h-annealed TFTs improved by a factor of ~3 compared to unannealed TFTs when the threshold voltage shift is extrapolated to 10 V. Stability at high temperatures with better lifetimes for the longer annealed TFTs is due to improvement in the a-Si:H/SiNx interface quality by the reduction of trapped charges inside the insulator. For all the TFTs at a positive gate bias, ΔVt follows a power law dependence with time, indicating state creation. A low β value (0.6 for unannealed TFTs to 0.37 for 96-h-annealed TFTs) indicates a good-quality a-Si:H channel and/or the a-Si:H/insulator interface after longer anneals.

We are reporting our results of Raman and X-ray diffraction (XRD) studies on amorphous Ge 46 S 54 thin films and the films after silver photodiffusion. Based on the Raman scattering studies, a structural model for amorphous Ge 46 S 54 is suggested including the formation of single Ge-S chains with a vibrational mode at 410 cm -1 . The result of XRD measurement indicates that there exists a medium-range order with about 6 A even at such Ge-rich composition. After the introduction of silver, the medium-range order is lost and there was a change in the diffraction curve indicative of the change in the local atomic order. The experimental results are explained in terms of our structural model, in connection with the application for fast switching memory devices.

With the increasing normative trend of clean indoor air laws prohibiting smoking in public places such as worksites and restaurants, the home is becoming the primary source of secondhand smoke (SHS) exposure. However, little empirical data indicate how SHS is distributed throughout homes and whether smoking in segregated areas offers protection. This project studied real-time data on levels of SHS in 9 homes in which smoking was permitted and in 3 smoke-free homes. Active sampling monitors were used to assess levels of PM(2.5), a marker for SHS, over a 3-day period. In smoking homes, one monitor was placed in the primary smoking area and another in a distal location, where smoking generally did not occur. Participants logged smoking and other activities that could affect air quality. In smoking homes, without assuming normality, the mean PM(2.5) level for the primary smoking areas was statistically significantly higher than that for distal areas (84 and 63 microg/m3, respectively). Both levels far surpassed the U.S. Environmental Protection Agency's annual standard of 15 microg/m3 for outdoor air quality. By contrast, the smoke-free home mean was 9 microg/m3, similar to outdoor air quality. These results suggest that the air in smoking homes was several times more polluted than that in smoke-free homes, regardless of where the measurements were taken, meaning that efforts to confine smoking to only part of the home offer no protection for people anywhere inside the home. Household members can be protected by implementing a smoke-free home policy.

We demonstrate how the radiation response and performance of Ag-chalcogenide glass radiation sensors fabricated on a flexible substrate can be optimized by modifications of spacing between electrodes.

Numerical simulations were used to study the transmittances (Ts) of ZnO/Al/ZnO (ZAZ) films with Al thicknesses between ∼1 and 40 nm. The simulations are validated using previously reported experimental results. Multilayers with Al thicknesses between ∼1 and 10 nm are shown to have average Ts between ∼75% and 90%, which decreased farther to ∼63 and 41% for the Al layer thicknesses of 20 and 40 nm, respectively. Variations in the ZnO thickness between ∼10 and 100 nm are shown to have little effect on the optical properties of the model multilayers for a given Al thickness. The reliability of the numerical simulations is tested by comparing them with experimental measurements on films produced using similar interlayer thicknesses. These are also shown to be comparable to the performance characteristics of indium tin oxide (ITO) anodes that are used currently in organic solar cells (OSCs) and organic light emitting diodes (OLEDs).

This study investigates the suitability of pure silver (Ag), pure aluminum (Al) and silver (3 at.%-aluminum) alloy (Ag(Al)) metallizations for potential application in programmable fuse links in field-programmable gate arrays. Single-line test-structures of the metallizations, of varying line widths (2.5–10 μm) on titanium nitride (TiN) and SiO 2 , have been investigated by subjecting them to extremely high current-density conditions. With increase in applied current densities, the lines experienced catastrophic failure. The microstructure and topography of the failed sites was examined using scanning electron microscopy and correlated with failure times. The failure mechanism for all three metallizations was dominated by Joule heating produced by the high currents flowing through the lines. For Ag and Ag(Al) structures on SiO 2 , failure occurs by Joule-heating-induced vaporization of metallization. In the case of Ag and Al metallizations on TiN, failure is due to vaporization of metallization followed by mechanical cracking of the barrier thin film due to thermal stresses that act on the layers.

Silver thin films (200 nm) were deposited on two different substrates, SiO2 and polyethylene naphthalate (PEN) by e-beam evaporation. The thickness of the Ag thin film on both substrates was determined to be 200 nm by Rutherford backscattering spectrometry. X-ray diffraction analysis showed that the coefficient of thermal expansion (CTE) of Ag on PEN (1.9 × 10− 5/°C) was the same as that of bulk Ag (1.9 × 10− 5/°C) while the CTE of Ag on SiO2 (3.1 × 10− 5/°C) was much larger than that of Ag on PEN. The results of our study indicate that the CTE of the Ag thin film is affected by the underlying substrate. In the case of Ag on PEN, the perpendicular and the lateral CTE were the same (1.9 × 10− 5/°C) because the Ag thin film expanded freely along all directions. In the case of Ag on SiO2, however, the lateral constraint of the thin film by the substrate caused anisotropic expansion and the apparent perpendicular CTE (3.1 × 10− 5/°C) was much larger than the apparent lateral CTE (0.54 × 10− 5/°C).

Semiconductor manufacturing economics necessitate the development of novel and innovative techniques that can replace the traditional time consuming reliability methods, i.e., the constant voltage stress time-dependent dielectric breakdown (CVS-TDDB) tests. We show that positive charge trapping is a dominant process when ultra-thick oxides are stressed through the ramped voltage test. Exploiting the physics behind positive charge generation/trapping at high electric fields, a fast I-V measurement technique is proposed that can be used to effectively distinguish the ultra-thick oxides' intrinsic quality at low electric fields. It will be demonstrated, based on experimental data, that our proposed technique can be a suitable replacement for the CVS-TDDB as a quality screening tool.

Polysilicon thin film transistors on flexible substrates are of considerable interest for applications in flexible displays. This paper investigates the formation of nanocrystalline silicon on flexible, transparent polymer substrates. An 800-nm layer of amorphous silicon was deposited on a polyimide substrate followed by a 20-nm layer of aluminum. Samples were rapid thermal annealed at 900 °C for 20 s, forming silicon nanocrystallites in a porous amorphous silicon film. The films were analyzed using Rutherford backscattering spectrometry, Raman Spectroscopy and cross-section transmission electron microscopy. A mechanism is proposed for the formation of silicon nanocrystallites and pores in the a-Si layer.

The effect of gamma radiation on low-temperature fabricated indium–zinc–oxide (IZO) thin-film transistors (TFTs) has been investigated. A negative turn-on voltage shift and sub-threshold swing degradation are observed after irradiation with a total dose of 1.7 Mrads from 60 Co. There is an increase in electron mobility from 2.8 to 8.8 cm 2 /V-s after the exposure. The changes in the electrical properties of these TFTs are attributed to the combined effects of interface states creation and electron–hole pair generation in the insulating layer. Better electrical reliability of the IZO TFTs over amorphous-silicon TFTs makes them promising candidates for space applications.

Ion beam analysis is used to analyze nickel and cobalt silicides formed in a cavity applicator microwave system with a magnetron power of 1200 W and a frequency of 2.45 GHz. Rutherford backscattering spectrometry, X-ray diffraction, four point probe measurements and rump simulation software are used to identify the silicide species present, phases, resistivities and layer thicknesses in samples processed in air, argon and evacuated mediums. Rutherford backscattering spectrometry is also used to confirm that the heating mechanism of the samples in microwaves appears not differ appreciably from that of conventional annealing. Electrical resistivity is used to explain microwave power absorption and demonstrate how to tailor a robust process in which thin film reactions can be attained.

We have developed a new technique for direct patterning and formation of cobalt silicide structures using focused ion beam implantation. This mask-free fabrication technique takes advantage of the influence on the kinetics of ion-beam mixing and properties of thin barrier oxides during silicide line formation. Silicide structures with dimensions of the order of 170 nm were produced on (100) silicon substrates. The process involves the ion implantation of 200 keV As++ through a thin cobalt film on SiO2/Si structure. A selective reaction barrier at the Si/Co interface comprising of a thin (∼2 nm) oxide (SiO2), prevents unwanted reactions with silicon. Ion-beam mixing was instrumental in fracturing of the oxide layer, thereby allowing the migration of metal atoms across the Si/Co boundary for the silicidation reaction to proceed during subsequent rapid thermal anneal treatments. Diffusion controlled reactions advanced rapidly in the implanted areas, requiring a two-step anneal sequence to inhibit reaction elsewhere. A threshold dose of 3×1015 cm−2 was required for process initiation. Four-terminal resistance test structures were formed for electrical measurements. Resistivity obtained ranged on the order of 12 to 23 μΩ-cm. Application of this method can facilitate a wide variety of silicide structures.

It is important for nanoscale transistors to have abrupt junctions, which are difficult to achieve via high-temperature anneals of implanted semiconductor layers due to undesired dopant diffusion. The use of a single-frequency microwave cavity applicator, along with a SiC-Alumina susceptor/assistor, is suggested as an alternative postimplantation process. Secondary ion mass spectroscopy analysis of microwave-annealed As-implanted Si samples show minimal diffusion, compared to rapid thermal annealed samples. Cross-sectional transmission electron microscopy and Raman spectroscopy confirm damage repair and Si recrystallization upon low-temperature microwave annealing (up to 650°C). Ion channeling and sheet resistance measurements validate dopant relocation and activation. The susceptor is used to provide surface heating to the high-atomic-number Z implanted sample to enable it to absorb microwaves and thereby recrystallize through volumetric heating.

We present the determination of the complex permittivity for low loss PCB material FR4 and high loss arsenic-doped silicon wafer in the GHz frequency range, based on closed-form analytical expressions employing the Bessel's functions. For convenience and economical reasons, the FR4 sample is cut from the commercial PCB as a sandwich disk of copper-dielectric-copper, while the bare silicon disk is contained in a prefabricated conducing cavity, referred to as the radial line cavity. Experimental measurements in support with the numerical analysis are also presented. Good agreement between computational results and laboratory measured data is observed.

Silver metallization is being investigated for potential use in future integrated circuits. Unlike the proposed copper metallization, Ag thin films can be reactive ion etched at reasonable rates using a CF4 plasma. This etch technology is an atypical ‘dry-etch’ process since the formation of volatile products is not the main removal mechanism. The primary film removal mechanism, however, is the subsequent resist strip process. The effects of process conditions on the etch rate and post-etch surface roughness is also characterized. Our study shows that the silver etch process in the CF4 plasma depends strongly on the reactive neutrals and the removal rate is enhanced significantly by the presence of energetic ions as well.

Silver-based metallization has been studied for a potential application as an electrically programmable fuse (eFUSE) device by local Joule heating induced at high current densities. Three different line widths (3.8, 6.3, and 10 mum) are investigated by subjecting them to extremely high current-density conditions. Based on short median lifetime and the topography of the failure sites, the dominant failure mechanism in Ag eFUSEs with TiN barrier layer under these current densities is examined. Evaporation times have also been calculated to correlate the Ag properties with the median failure time. The barrier layer has an important role to play in determining the failure time in these types of eFUSEs.