Polysilicon Material Research Articles

Modeling and Design Parameter Optimization to Improve the Sensitivity of a Bimorph Polysilicon-Based MEMS Sensor for Helium Detection.

Helium is integral in several industries, including nuclear waste management and semiconductors. Thus, developing a sensing method for detecting helium is essential to ensure the proper operation of such facilities. Several approaches can be used for helium detection, including based on the high thermal conductivity of helium, which is several times higher than air. This work utilizes the high thermal conductivity of helium to design and analyze a bimorph MEMS sensor for helium sensing applications. COMSOL Multiphysics software (version 6.2) is used to carry out this investigation. The sensor is constructed from poly-silicon and SiO2 materials with a trenched cantilever beam configuration. The sensor is electrically heated, and its morphed displacement depends on the surrounding gas's composition, which decreases in the presence of helium. Several factors were investigated to probe their effect on the sensor's sensitivity to helium, including the thickness of the poly-silicon layer, the configuration of the trench, and the thickness and location of SiO2 layer. The simulations showed that the best performance, up to 2 ppm helium detection level, can be achieved with thinner beams and medium trench lengths.

Comparative Study of Cantilever Biosensor for Detection of Tuberculosis

Abstract: Now everywhere in the world sensors are used to solve daily human problem. In the medical field sensors are used to diagnose various diseases. In this article for detection of tuberculosis, micro cantilever biosensor has been design and simulate. Rectangular shape cantilever biosensors with silicon, poly-silicon and aluminium material were designed and analysed the displacement. The displacements of this biosensor are compared with the other available models. The MEMS based micro cantilever biosensor were design in COMSOL Multiphysics. 10N to 100N load force are applied on the surface of cantilever for deliberate the interaction of antigen antibody. Stress generated on the surface of cantilever when antigen antibody binds together and it get deflects. This deflection is measured for 10N to 100N load force which is compare with other modules. The displacement generated by cantilever was 1.71 x 1028 µm for 100N force which is higher than all the other models, thus the proposed cantilever model is the best model for detection of tuberculosis

Simulation of Cantilever Biosensor for Detection of Tuberculosis

Abstract: Worldwide Mycobacterium Tuberculosis comes under top ten diseases, which affect to millions of people every year. Due to its complicated structure, it is very difficult job to diagnose this infectious disease in time. In this research article, first the complications of tuberculosis and some detection techniques are studied. After that, for fast and within time detection of tuberculosis, Cantilever Biosensor with various shapes are simulated. The Cantilever is design with Poly-Silicon material and its surface coated with ESAT-6 antigen antibody. For stress generation a load forces are apply from 10N to 100N and displacement of all the models are analyze. After analysis it has been recorded that Rectangular shape generates maximum displacement as compare with other shapes. Rectangular shape cantilever biosensor achieved 1.71 x 1028 µm displacement with 100N load force. Keywords: Cantilever, Mycobacterium Tuberculosis, Biosensor, COMSOL, Displacement, Rectangle, Simulation.

An ultrafast temperature response analysis of a MEMS-based igniter using the finite-element method

This study reports the simulation and experiments of a MEMS-based igniter for a semiconductor bridge (SCB), which is fabricated using complementary metal oxide semiconductor technology. The finite-element method was first employed to simulate the ultrafast temperature response of the ignition process of SCB under conditions of an electro-exploding ignition, electro-thermal ignition, and no-ignition and to conduct a capacitor discharge stimulation. The recorded voltage from an oscilloscope was used as the initial condition, and conductivity values based on experimental data were taken as a key parameter for the polysilicon material to ensure the accuracy of the heat source loaded into the model. Under the electro-exploding ignition, the SCB was initially ignited at the sharp corners at the valley of the first voltage peak instead of the secondary peak. The maximum temperature of the SCB was no more than the melting point of the polysilicon material (except for the sharp corners) and only at 1369 ​K under the electro-thermal ignition and no-ignition conditions, respectively. The optical testing and ablation results of the bridge area demonstrate that the numerically simulated temperature is quite accurate. This method can be easily extended to other MEMS-based igniters for temperature prediction applications.

UMG silicon for solar PV: From defects detection to PV module degradation

Upgraded metallurgical grade silicon (UMG-Si) for photovoltaic (PV) solar applications has been manufactured through the metallurgical route by means of the process developed by Ferrosolar. In an ambitious mass production test, performed in commercial solar cells and modules production lines, the silicon was proven to be appropriate for photovoltaics applications (Forniés et al., 2019 Mass production test of solar cells and modules made of 100% umg silicon. 20.76% record efficiency. Energies 12), reaching, in a conventional production line, up to 20.76% of solar cell efficiency with multicrystalline cells made of 100% UMG silicon. In this paper we present more results from the mentioned massive test. Defect engineering is being applied to improve the bulk lifetime of the UMG wafers and to guide in the identification of the limiting defects in the material. Moreover, the modules produced with 100% UMG silicon solar cells were installed together with the modules produced in the same production line with polysilicon material to assess the degradation of the UMG silicon when compared to polysilicon. After 24 months of outdoor PV generation, the degradation, in terms of Performance Ratio at 25 °C (25PR) diminution, has been the same for both types of modules. Additionally, a Life Cycle Assessment (LCA) has been performed for this UMG silicon and state-of-the-art Siemens polysilicon to compare the environmental impact of both silicon feedstocks. The results presented in this paper; chemical analysis of wafers, defect engineering, low degradation, average efficiency and environmental assessment, lead to a complete study of UMG silicon, confirming its potential to be used as raw material for PV applications.

Electrothermal micro tweezer for biomedical applications

This paper presents design, simulation and results analysis for a novel micro tweezer. The principal element in the proposed device is a double U-beam electrothermal actuator. Using FEM tool, Poly-Silicon material is applied to the device structure and analysed for both in-plane and out of plane displacement for respective range of actuation potential. The micro tweezer holder mouth provided a maximum in-plane displacement of ∼48µm at 4.5V actuation voltage. Comparatively negligible out of plane displacement exhibited by the device during simulation. The proposed micro tweezer is designed for the micromanipulation of biological cells in a better way.

Design of Piezo-Resistive Type Acoustic Vector Sensor using Graphene for Underwater Applications

In recent years as the level of radiated noise of submarine drastically got decreased, the requirement of underwater acoustic sensor has become essential for the detection of low frequency acoustic signal. The latest advancement in the field of underwater sensors is the Micro Electro Mechanical Systems (MEMS) sensor. The major advantage of this sensor being determination of directionality along with the measurement of pressure of an acoustic signal. The biological inspiration behind the design of the sensor was derived from fish lateral line sensing system, with piezoresistive transduction principle to obtain the objective of miniaturization and low frequency signal detection. In this paper, we are reporting the design, simulation of an underwater two-dimensional MEMS acoustic vector sensor which exhibits better sensitivity, flexibility when compared to the traditional acoustic vector sensor. In this work, thin film of piezoresistve material, Reduced Graphene Oxide (Rgo) is taken as pressure sensing element instead of traditional polysilicon material and its performance in terms of sensitivity and directivity is analysed. MEMS acoustic vector sensors using Reduced Graphene Oxide and polysilicon were simulated on flexible kapton and silicon substrate respectively using COMSOL Multiphysics 5.5 vesrion. The simulation results indicates that designed vector sensor based on MEMS technology and piezoresistive effect of rGO on flexible kapton substrate is feasible and possesses better sensitivity of -149.47 dB when compared to the sensitivity of -171.37 dB of polysilicon based traditional acoustic vector sensor. The simulated value of eigen frequency of the sensor is found as around 47Hz, which almost matches with the theoretical value of resonance frequency of the sensor as per the design considerations of the sensor and hence capable of detecting low frequency acoustic signals.

A Simulation Study for Optimizing Grain Size in Poly-Crystalline Silicon Material Using Impedance Spectroscopy

This paper uses impedance spectroscopy as a simulation tool to analyze grain boundaries properties in poly-crystalline materials. The interfacial structure at grain boundaries in poly-crystalline materials plays a decisive role in their electrical behaviors and degrades the performance in integrated circuits, gas sensors and solar photovoltaics. A numerical simulation is carried out to optimize grain size of poly-crystalline material to behave as mono-like material using impedance spectroscopy technique. The grain boundary potential (Vb) obtained from thermionic emission diffusion theory based continuum and localized energy models are utilized for obtaining the resistance (R), capacitance (C) and angular frequency (??) of the bulk of the grain (Rb, Cb and ??b) and that of grain boundaries (Rgb, Cgb and ??gb) using the brick layer model. Two markedly different impedance spectra are obtained, one for the bulk of the grain and another for the grain boundaries. It is found that with an increase in the grain size (Lg), the signatures of grain boundaries spectra diminish and at a particular grain size, disappear completely which indicates that the poly-silicon material behaves comparable to mono-crystalline material. In this simulation work, silicon material is taken as the reference due to its abundant availability and huge market potential for photovoltaic and semiconductor applications but the simulation can be implemented on any poly-crystalline materials. The effect of varying silicon material resistivity (1.0???3.5 ??cm) and temperature (300-420 K) on grain size was also analysed using the impedance spectra. The findings of the paper will be helpful for the silicon ingot growth industries to decide the optimum grain size during the polysilicon materials growth.

Performance evaluation of superjunction UMOS with dual polysilicon gate

A modified Superjunction (SJ) UMOS employing dual polysilicon material that is P+ polysilicon and N+ polysilicon on lower and upper portion of gate respectively is proposed in this paper. The proposed structure exploits the advantage of workfunction engineering at the gate electrode. The workfunction variation along the channel leads to increment in the transconductance and reduction in on resistance. The electrical characteristics of conventional SJ UMOS and proposed SJ UMOS have been simulated using ATLAS. The simulation results reveal 14.1% reduction in the resistance without any degradation in breakdown voltage. Further, transconductance and Baliga's Figure of Merit has also been calculated indicating 25% and 16.4% increment respectively for proposed structure signifying enhanced performance. The impact of temperature on the device behavior is also analyzed and it is suggested that the proposed device performs better than the conventional device even at higher temperature.

Thermoelectric properties of nanostructured porous-polysilicon thin films

Abstract In this paper, we address the optimization of the electrical and thermoelectrical properties of nanostructured polysilicon material for integration in thermoelectric (TE) devices. In particular, we describe an original method to build a superficial and nanostructured porous polysilicon (POpSi) thin film on a Silicon substrate. This latter is electrically isolated from the conductive Silicon substrate by an SiO2 interlayer for Van der Pauw electric and home-made thermoelectric measurements. From the characterization data, we demonstrate that the nanostructuration brought by porosification of polysilicon layers (polySi) breaks their thermal conductivity by a factor of about 30 and has no detrimental impact on their Seebeck coefficient: a POpSi with up to 62% porosity has an experimental Seebeck value of 260 µV/K when the standard polysilicon, it is built from, is n type with a carrier density of 3.4 × 1019/cm3. On the other hand, the benefit of the thermal conductivity reduction clearly over-compensates the degradation of the experimental electrical conductivity measured in the POpSi layers: in terms of the figure of merit ZT, a 25-fold increase in a POpSi layer with 44% porosity is seen compared to the standard polySi layer (it increases from 0.004 to 0.1). Such a novel material is a viable candidate for planar thermoelectric devices using Silicon technologies. In this effort, we discuss the integration of a POpSi thin film with optimum porosity into a planar TE microgenerator (µTEG) with suspended membranes supported by a simulated conversion efficiency increased by 28% compared to a µTEG integrating the standard polySi layer counterpart.

Effects of nano‐grain structures and surface defects on fracture of micro‐scaled polysilicon components

AbstractThis study examines a simple fracture model for microscopically heterogeneous polysilicon components when Griffith theory applicable only to homogeneous materials fails. The strength‐limiting micro/nano‐ surface defect a0 is linked to the nano‐scaled grain size G of polysilicon and bulk fracture properties. Here the a0/G ratio is not large enough for polysilicon to be considered as homogeneous. Two polysilicon materials, with laminated grain structures (G = 125 nm) and columnar grain structures (G = 285 nm), have been analyzed. The simple fracture model together with a normal distribution methodology can be used to predict both the mean and 96% reliability fracture curves for the micro/nano‐crack range bridging the classic Griffith theory and the non‐linear fracture model.

Study on the adsorption mechanism of benzoylurea insecticides onto modified hyperbranched polysilicon materials.

Several hyperbranched polysilicon (HBPS) materials with different end group modifications were designed and synthesized and the structures were characterized. The modified HBPS polymers were applied to the adsorption of benzoylurea insecticides (BUs). The binding mode and binding energy between the HBPS and BUs were quantified and the results of an adsorption kinetics study and an adsorption thermodynamics experiment were verified by calculation and mutual verification. The adsorption mechanism of BUs onto HBPS was also discussed. The theoretical results show that the most effective way to combine the adsorbent and BUs is via hydrogen bonding when the end group is an amino group. Moreover, the most effective combination when the end group is β-cyclodextrin is the interaction of the BUs with the interior of the cavity to form a host–guest coating. The theoretical results of other end group-modified HBPS materials were also obtained and verified by adsorption experiments. In this work, an experimental method for obtaining the binding mode by theoretical calculations and then verifying it according to adsorption experiments was established.

Finite element analysis of polysilicon based MEMS temperature-pressure sensor

Temperature and pressure sensor, both are in high demand for industrial application but to use pressure sensor in harsh environment is a challenging task. As many of the semiconductor devices have low tolerance to heat and device failed to work. To overcome the failure of the device, many attempts have been taken by researches. The one cost effective and efficient method is utilization of polysilicon material. In this paper, we investigate the opportunity of utilizing p-polysilicon for temperature-pressure sensor. To better understand the effect of pressure on resistors the device has been designed and modelled using finite element analysis and virtual fabrication process of proposed sensor has also been shown. The finite element analysis shows the cause of variation in sensitivity and temperature drift due to the influence of pressure. The sensors have been loaded under the pressure ranging from 10 to 100 psi within the temperature range from −40 °C to 60 °C. The sensitivity of proposed model was found to be ∼1.063 mv/psi. The change in resistance for lower pressure shows a drift in output curves while for higher pressure the output curves varies linearly with respect to temperature. The TCR value of designed pressure sensor was found to be ∼5.477 × 10−3(°C)−1.

Stress and Deformation Analysis of Piezoresistive Square Diaphragm Nano Pressure Sensor

Pressure sensors are among the most widely used MEMS product as sensors in commercial and industrial applications. The diaphragm structure, thickness, and dimensions along with the placement, size, and shape of the piezo resistors are important in the process of designing a pressure sensor. This paper presents the design and simulation of the square diaphragm to analysis the deformation and stress of various materials as well as for the different thickness of the diaphragms at low pressure in the range of 0.1 to 1.5 bar. The design of diaphragm is as a 10 μm thick square diaphragm with 800 μm edge length are considered, which were analyzed by using ANSYS 17 software. The results show that deformation and stress reduction as in the increase in the thickness, which is directly related to the performance of the diaphragm. CNT based diaphragm also showed the improved performance of the pressure sensor as compared to the silicon and polysilicon material.

A computational study of the effect of bond pad thickness on the polysilicon piezoresistivity due to wafer level probing

Polysilicon is an integral part of many devices in all CMOS processes. Circuit Under Pad (CUP) devices are required to have consistent and accurate electrical performance just like any other device. This paper presents an investigation on stress impact of probe insertions on two bond pad metal options (METMID and METTHK) on a polysilicon resistor placed under the bond pad. Wafer level probing results in residual stress on both Back End Of Line (BEOL) as well as Front End Of Line (FEOL) structures. This residual stress would impact the electrical properties of the polysilicon material used in such devices. In this study, such electrical impact is measured in terms of change in resistance (piezoresistivity) of a polysilicon resistor which was placed underneath the bond pads. A commercial finite element analysis software (Comsol Multiphysics) was used to predict the stress distribution in the polysilicon device, followed by experimental validation of the electrical resistance. It was observed that the bond pad thickness can influence the residual stress which in turn causes a change in resistance after wafer level probing. However, for each bond pad thickness, multiple probe insertions did not significantly change the resistance of the device placed under the bond pad.

Dual-frequency CMOS terahertz detector with silicon-based plasmonic antenna.

Multi-frequency Terahertz (THz) detectors have shown great application potentials in THz imaging and sensing systems. For the first time to our knowledge, a novel dual-frequency THz detector with the stacked structure consisting of a silicon-based plasmonic antenna and a metal-based antenna in one compact unit is proposed and fabricated in standard CMOS technology. Compared with the metal antenna, the antenna based on heavy-doped poly-silicon materials enables the detector to excite localized surface plasmon resonance mode, making the effective absorption of the THz waves and thus resulting in the significant responsivity enhancement of the detector. The experimental results show a maximum voltage responsivity up to about 2000 V/W and 450 V/W, while the noise equivalence power is as low as 23 pW/Hz0.5 and 110 pW/Hz0.5 for the silicon antenna and metal antenna at the frequency of 220 GHz and 650 GHz, respectively. The presented dual-frequency detector can be easily implemented in a small size in favor of high-density array integration.

Optimization of Processing Parameters for Water-Jet-Assisted Laser Etching of Polycrystalline Silicon

Liquid-assisted laser technology is used to etch defect-free materials for high-precision electronics and machinery. This study investigates water-jet-assisted laser etching of polysilicon material. The depths and widths of the etched grooves were investigated for different water-jet incident angles and velocities. To select optimal parameters for a composite etching processing, the results of many tests must be compared, and at least one set of good processing parameter combinations must be identified. Herein, the influence of different parameters on the processing results is studied using an orthogonal test method. The results demonstrate that the depths and widths of the processing grooves were nearly identical at water-jet angles of 30°and 60°; however, the 60° incidence conferred a slight advantage over 30° incidence. The section taper, section depth, and surface topography were optimized at a water-jet velocity of 24-m/s, 1.1-ms laser pulse width, 40-Hz frequency, and 180-A current. Under these conditions, the section taper and groove depth were 1.2° and 1.88 mm, respectively. The groove surfaces exhibited no splitting, slagging, or other defects, and no recast layers were visible.

Sensitivity enhancement and temperature compatibility of graphene piezoresistive MEMS pressure sensor

MEMS pressure sensor has shown a remarkable change in revenue collection during the year 2018. Due to recent growth in smart microsystem technology for automation systems, demand has grown substantially for sensors. High sensitivity, flexibility, miniaturization and bulk production are some of the key factors of a pressure sensor in achieving new heights in the MEMS market. In this paper, Graphene piezo resistive material has been analysed for pressure sensing elements and compared with Polysilicon in terms of sensitivity and sensor performance degradation at different temperature. MEMS pressure sensors using Polysilicon and Graphene piezo resistive materials were simulated on silicon (100) substrate by COMSOL Multiphysics 5.3a version. The simulation result shows that at room temperature polysilicon pressure sensor performs well with pressure sensitivity of 3.81 mV/psi as well as it is found that graphene pressure sensor also shows better results at room temperature showing a pressure sensitivity of 3.98 mV/psi. As on frequently increasing the temperature it is noticed that polysilicon pressure sensitivity degrades with a factor of 0.64 mV/psi. However, graphene pressure sensor shows very less variation in sensitivity at higher temperature. Although it shows a small increment of 0.02 mV/psi in the pressure sensitivity. This analysis opens the path to utilise the graphene pressure sensor at high temperature.

Investigation of wavelength effects on polycrystalline silicon damages using nanosecond pulse laser irradiation

Based on polyvinylidene fluoride(PVDF) piezoelectric sensing technology, this paper investigated the damage mechanism of polysilicon irradiated by three wavelengths (1064 nm, 532 nm, and 355 nm) of nanosecond pulsed laser. According to the damage characteristics of the polysilicon, the thermal shock damage mechanism of laser irradiation on polycrystalline silicon has been studied, and the propagation law of laser shock waves in the brittle materials has been explored. The results show that the melt spatter phenomenon of the polysilicon surface is caused by melting from the heat generated when the material absorbs high-energy laser photons, combined with the vapour pressure and plasma pressure. The main cause of the polysilicon material’s cleavage and destruction is the laser thermal stress. The corrugated field around the material’s radiation area is mainly the result of the coherent coupling of optics and thermodynamics. The peak value of the laser shock wave in polysilicon shows a linearly distributed attenuation.

(Invited) Dual-Gate TFT for Chemical Detection

Field effect transistors possesses many advantages for chemical detection. As their electrical characteristics strongly depend on electrical charges located on their surface, they are able to measure with good sensitivity and very precisely any variation of charges concentration of the surrounded media. They can be easily integrated, are low-cost and provide a rapid and reliable result. The main application developed here is the pH measurement. In this case, the gate contact is removed and replaced by a liquid polarized by a reference electrode, leading to the ISFET technology. Those structures can also be developed by using a thin-film technology. The technology we developed is based on LPCVD polysilicon, silicon oxide and nitride deposited by CVD. The sensitivity of ISFET or ISTFT is limited by Nernst equation, but can be enhanced by using dual-gate structures. In this technology, capacitive enhancement can be optimized by choosing specific thicknesses and materials for back and top gates. In this case, the sensitivity enhancement is theoretically given by the ratio of the top gate capacitance to the back-gate capacitance. This technology has been developed also by using thin-film transistors from polysilicon material. Several structures have been developed in order to obtain good electrical performances for field-effect transistors, as low threshold voltage and good electrical characterization for back and top gates. Those characteristics are controlled by a good choice of insulator, and a thickness optimization. Transistors are characterized with different polarizations; in back-gate, top-gate and dual-gate operating modes. Capacitive enhancement in determined for the different cases and compared to theory. Transistors are then used for chemical detection, especially with measurement of pH. ISFET is already highly used for pH measurement, but its sensitivity is limited to 59 mV/pH. By using a dual-gate structure, this sensitivity can be substantially enhanced. The developed structures, based on previous studies of dual-gate TFTs, includes a back-gate contact, and an integrated electrode at the surface for the top-gate liquid polarization. Threshold voltage are measured and optimized. A slight doping of the active layer induces a decrease of the threshold voltage, necessary in the case of measurement in liquids. Sensitivities for pH measurement are compared with theory and show the capacitance enhancement. Figure 1