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Micromachined, piezoresistive-sensed diaph- ragms are designed and fabricated specifically for infrasound sensing applications. Relatively large diaphragms, up to 6 mm $\times6$ mm, are fabricated to meet the high sensitivity requirements of infrasonic monitoring. A double-stack SOI wafer process is used, resulting in a streamlined two-mask process without the need for doping or ion-implantation. Pressure-sensitivities of diaphragms are studied using a custom static calibration set-up. The piezoresistance of longitudinal and transverse resistors are studied over a large pressure range of ±5,500 Pa so that the linear and nonlinear response regions of diaphragms are observed. Measurements are compared against a nonlinear finite element simulation—shown to accurately predict the sensor’s behavior over a large response range. [ABSTRACT FROM AUTHOR]

A shear-stress or skin-friction sensor for hypersonic flow measurements is presented. The sensor measures the displacement of a spring-mounted rectangular plate using a differential capacitance-based detection scheme. The 1.8-mm $\times $ 1.8-mm sensor is fabricated using a silicon-on-insulator wafer with a 20- $\mu \text{m}$ -thick epitaxial layer and packaged into a cylindrical form-factor with a 1/4-in diameter. Wall-shear-stress measurements are performed at a Mach-2.3 supersonic wind-tunnel facility at The University of Arizona. The sensors observe several features anticipated from hypersonic/supersonic flow physics, including the passing of normal shocks and the reversal of measured shear polarity when flow separation is deliberately induced via the use of a compression ramp. Furthermore, the measured value for dc wall-shear stress agrees with the model predictions for fully developed turbulent boundary layers. [2018-0191] [ABSTRACT FROM AUTHOR]

A microelectromechanical-system piezoelectric pressure sensor targeting hypersonic flow applications is presented. The sensing diaphragms have 500- $\mu \text{m}$ diameter and are comprised of a composite stack of Si, SiO2, and AlN. This paper presents the fabrication and packaging details of the sensor and then presents test results from a Mach-6 hypersonic-flow facility, in which the prototype sensor data are compared against data from a mature commercial sensor present in the same tests. Salient hypersonic-flow features are observed in signals captured by the prototype. The package is comprised of an on-chip two-element array with 650- $\mu \text{m}$ pitch, and signals from the elements captured during hypersonic-flow tests are highly correlated. [2018-0196] [ABSTRACT FROM AUTHOR]

Sol-gel derived nano-sized glass frits were incorporated into the Ag conductive ink for silicon solar cell metallization. This mixture was specifically formulated for inkjet printing on textured Si wafers with 80 nm thick SiN x anti reflection coating layers. The correlation between the contact resistance and interface microstructures were studied using scanning electron microscopy and transmission electron microscopy. In addition, the specific contact resistance between the front contact and emitter was measured at various firing conditions using the transfer length model. On an emitter with the sheet resistance of 60 Ω/sq, a specific contact resistance below 5 mΩ cm2 could be achieved at a peak firing temperature around 800 °C. We found that the incorporated nano-glass frit act as a very effective fire through agent, and an abundant amount of Ag crystallites was observed along the interface glass layer. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We developed a novel cost effective process scheme for the fabrication of highly efficient selective emitter solar cells, which uses a laser doping method combined with an etch back process. The laser doping process using a 150 ns pulse width green (532 nm) laser effectively controls the doping profiles to form a selective emitter. However, laser damage was created on the laser-doped surface and eventually the performances and stabilities of laser-doped cells were degraded due to this damage. Using a transmission electron microscope (TEM), the damage was examined and found to have a thickness of 40 nm of amorphous silicon. This thin damage layer was effectively removed in an acid mixture solution. The combined process of laser doping and etch back is called the laser etch back process. After removal of this thin damage layer, the cell efficiencies were significantly improved up to 19.17%. [ABSTRACT FROM AUTHOR]

Deep reactive ion etch (DRIE) processes are performed on both sides of a silicon-on-insulator (SOI) wafer to realize piezoelectric accelerometers consisting of 20-\mum-thick epitaxial silicon cantilevers with bulk silicon masses at the tip. Sol-gel deposition of lead-zirconate-titanate (PZT) is used to realize an 800-nm-thick film on the top surface of the beams. Prior to accelerometer characterization, a system identification procedure based on laser Doppler vibrometry is performed, providing a complete description of the devices and predicted sensitivities. Frequency response measurements confirm device sensitivities in the 3.4–50 pC/g range in the flat-band (depending on device geometry), and resonance frequencies in the 60-Hz–1.5-kHz range. The self-noise for the longest beam of 8.5 mm is measured as 1.7 \mug/\sqrtHz at 30 Hz and is limited by dielectric loss of the PZT film which is estimated to have a \tan\delta of 0.02. Scaling relationships for this particular device geometry are presented to provide insight into possible future design directions. \hfill[2012\--0300] [ABSTRACT FROM PUBLISHER]

A 29.4-W \(X\) -band high-power amplifier has been substantialized using GaN on high-resistive silicon substrate. The developed GaN high electron mobility transistor (HEMT) with 3.6-mm gate periphery provides 29.4-W output power and 8-dB small signal gain at 8 GHz with power added efficiency of 39.4% under pulse condition at a duty of 10% with a pulsewidth 100 \(\mu \) s. Load-pull measurement at 8 GHz demonstrates an output power density of 8.1 W/mm. To the best of our knowledge, the presented amplifier exhibits the highest power density, delivering \(>10\) W of output power in \(X\) -band for GaN HEMTs technology on silicon substrate. [ABSTRACT FROM AUTHOR]

We investigated the field degradation modeling of potential-induced degradation (PID) in crystalline silicon photovoltaic modules. Five accelerated tests using four-cell mini modules were conducted to derive the hourly degradation rate of the potential induced degradation. The voltage-Peck model was used for predicting the hourly degradation rate. The field degradation modeling was performed at Busan and Miami. The annual degradation rate in field based on the temperature, humidity, and solar irradiance was calculated as the sum of the hourly degradation rate for one year. The annual degradation rates in Busan and Miami were recorded as 6.93% and 11.23% under 72cells and 18 modules series-connected string configuration, respectively. The annual degradation rate induced by PID in the solar power plant in Busan showed similar result to 8.8%. [ABSTRACT FROM AUTHOR]

The temperature variation of solar cells due to white bias light irradiation during the spectral responsivity measurement and its effect on the spectral responsivity measurement result were investigated for various types of solar cells, such as crystalline silicon (c-Si), Cu(In,Ga)Se 2 (CIGS), and dye-sensitized solar cells (DSSCs). For the investigation, a spectral responsivity measurement system, which can employ the well-known sample temperature control methods (such as the “temperature controlled sample stage” method and the “forced air cooling” method) has been used. Hence, the availability of these sample temperature control methods has also been tested. Through the investigation, it was found that the actual temperature of the solar cells located under the AM1.5G-approximated white bias light can be increased significantly during the spectral responsivity measurement, depending on the sample temperature control methods applied. In addition, it was also found that the increase of sample temperature can lead to a significant error in the measured spectral responsivity, depending on the types of solar cells being measured. In addition, a simple analytic model based on the classical heat transfer theory was developed to understand the temperature variation of the solar cells under the spectral responsivity measurement environment. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we present numerical and experimental analyses of the effect of the work function of the transparent conducting oxide (TCO) on the performance of silicon heterojunction solar cells. The simulation results showed that the solar cell performance such as V oc and FF were strongly affected by the work function of TCO films due to band bending. The experimental analysis was carried out by preparing Zn–In–Sn–O films with varying work function by varying the composition. The compositional dependence of the work function, optical and electronic properties of Zn–In–Sn–O films was examined, and the performance of the silicon heterojunction solar cells with corresponding TCO films was analyzed. The electrical properties and work function in Zn–In–Sn–O films were significantly influenced by Zn content, and Zn–In–Sn–O film with 12.7 at.% Zn content, which had the highest work function and lowest resistivity among the studied films, resulted in the highest conversion efficiency of solar cell due to increased V oc and FF. It was shown that the behavior of performance parameters in silicone heterojunction solar cells closely correlated with the work function and electrical properties of TCO films. [Copyright &y& Elsevier]

Abstract: High efficiency solar cells require good back surface field passivation and high back reflectance in the rear Al region. In module processes, wafer-based solar cell can break through stress during soldering uneven rear aluminum surfaces - a serious problem that affects throughput. This work examined rear surfaces with respect to controllable process factors such as ramping and cooling rates during rapid thermal processing, and the fineness of aluminum powder used in the screen-printed paste. A faster ramp up rate resulted in a uniform temperature gradient between the aluminum and silicon surfaces. As a results, the bumps on the aluminum surface were small and of high density. Fine aluminum metal powder in the paste for screen-printing contact points resulted in large distribution, high density bumps. Bumps formed during cooling in metallization, their sizes and densities were dependent the on uniformity of the aluminum and silicon liquid wetting of the silicon surface. [Copyright &y& Elsevier]

Abstract: When amorphous silicon thin film is deposited on n-type c-Si substrate, partial epi-layer of silicon grows mainly on the valley of the pyramid where two (111) planes meet. The epi-layer degrades a-Si/c-Si interface properties. This is the main cause which leads to a decrease in the efficiency of silicon heterojunction solar cells. In this study, we made various texture shapes of silicon substrate for heterojunction solar cells with n-type silicon wafers. Four different types of textures on silicon heterojunction were prepared: large textured, smoothened large textured, small textured, and smoothened small textured. Surface texturing is well known as one of the major paths to improving the efficiency of silicon solar cells by increasing the short-circuit current through effective photon trapping. The results were successful for silicon random texturing using potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) solutions. Silicon heterojunction solar cells were fabricated on textured substrates, indicating the feasibility of KOH and TMAH texturing for solar cell fabrication. We obtained images of the surface morphology using a scanning electron microscope. The interface cross-section was taken using a transmission electron microscope. We gained the optimized surface morphology of silicon substrate for a-Si/c-Si interface in silicon heterojunction solar cells. [Copyright &y& Elsevier]

For application of copper metallization to silicon solar cells, electrical resistivity of the electroplated Cu was investigated for different annealing conditions: the rapid thermal annealing (RTA) and the vacuum annealing at various temperatures. The characteristics of Ti as the diffusion barrier were also observed. The specific contact resistance between Si and Ti/Cu was measured using Kelvin test pattern. For 8-min electroplated sample, the lowest resistivity of 2.1 μΩ cm was obtained at 300°C RTA condition. For Cu with Ti barrier, 400°C 2 min vacuum-annealed sample showed etch pits whereas 400°C RTA showed no etch pits. A vacuum annealing at 450°C for 30 min reduced the specific contact resistance to 7.2×10−6 Ω cm2. [Copyright &y& Elsevier]

Abstract: The effects of the size and density of a pyramidal texture, as formed on the surface of Si solar cells to increase the light trapping efficiency, on the optical reflectance and absorptance were examined by comparing simulation results and experimental observations. A ray tracing algorithm capable of the direct calculation of the absorbed energy in active Si was utilized for the simulation. The simulation results showed that the optical reflectance spectra, i.e., the absorptances, of the textured surface with a fixed density of pyramids were not affected by the pyramid pitch, whereas the spectra with varying density of pyramids decreased with an increase in the density of the pyramids. Observations similar to the simulation results were observed from the experimentally textured surfaces, indicating that the density of the pyramid area, i.e., the area of the flat region, is the most crucial factor affecting the optical behavior of a textured Si surface with three-dimensional pyramid patterns. [Copyright &y& Elsevier]