Papers by Keyword: Poly-Silicon

Abstract: Polysilicon is a very attractive material in microelectronics for thermal sensors. In this paper, the effect of humidity on thermal resistance of surface micromachined polysilicon is invested. It is found that the thermal conductivity variation of air due to humidity changes the suspended polysilicon resistor evidently. This property could be used as the working principle of relative humidity sensor.

Abstract: Many new methods for polysilicon texture are invented in solar cell preparation and isotropic acidic corroding has become one of the primary methods for its advantage of fitting for mass production. It is an unavoidable problem that how to evaluate results under different reagent ratio and different reaction time. On the base of Genetic Algorithm (GA), methods for evaluating the best process parameters are given out aided by artificial neural network (ANN), It is proved by experiments that this method can find out the best combinations of process parameters globally.

Abstract: The recent explosive growth of Photovoltaics and the relative avidity for silicon of the predominant solar cell technology have resulted in a dramatic change of the polysilicon industry structure. While in the past the polysilicon was manufactured almost exclusively for the semiconductor industry, now more than half of the market is devoted to the solar industry. The different alternative routes to purify silicon for photovoltaic applications are presented in the paper, analysing their advantages and drawbacks. Emphasis is made on the CENTESIL initiative, a new private-public partnership venture promoting a pilot plant that is in an advanced state of construction. The goal is to allow the photovoltaic companies worldwide to count with an independent research centre to help them to establish their own polysilicon plant.

Abstract: A novel method for growing highly-crystalline 3C-SiC on an oxide release layer via a poly-Si seed layer is reported. Silicon carbide’s potential role as a ubiquitous material for MEMS fabrication lies in its dual role as an electronic and mechanical material. Unfortunately, due to residual stresses and crystal defects stemming from the large lattice constant mismatch and the thermal expansion coefficient difference between SiC and Si, the use of SiC in Si-based MEMS fabrication techniques has been very limited. The growth of 3C-SiC on a poly-Si seed layer deposited on oxide on (111)Si substrates (i.e., p-Si/ SiO2/(111)Si) provides an alternative fabrication method to expensive, traditional SOI bonding techniques for producing free-standing 3C-SiC MEMS structures. 3C-SiC grown with a poly-Si seed layer on SiO2 should experience reduced residual stress and far fewer defects due to the compliance of the SiO2 layer. Although poly-Si is utilized as a seed layer in this process, a well-ordered monocrystalline 3C-SiC layer was achieved and the process and film properties reported.

Abstract: A design and simulation of a fully CMOS compatible micromachined multilayer cantilevers-based environmental thermometer are presented. The operation principle of the structure is depending on the mismatch effect of thermal expansion coefficient and the piezoresistive effect of polysilicon in CMOS process. Upon temperature variation, the deformation of the multilayer cantilever resulted from the large thermal expansion coefficient mismatch of different materials can be sensed and translated to an electrical voltage output by using a symmetric piezoresistive Wheatstone bridge. The mechanical characteristics of the device are analyzed with the extension of bi-layer Timoshenko model and the output of the read-out circuit is also simulated. The calculation and simulation show that the device with bi-direction deformation may have wide temperature range from -100 to 100°C and sensitivity about 0.15mV/°C, which fit the demand of radiosonde for environmental temperature measurement. This sensor may also have other favorable features, such as micro size, low-cost due to its working principle and compatibility with commercial CMOS process.

Abstract: The gauge factor and nonlinearity of 80nm polysilicon nanofilms with different doping concentration were tested. The experimental results show that, from 8.1×1018cm-3 to 2.0×1020cm-3, the gauge factors first increase then decrease, which like the common polysilicon films (thickness is larger than 100nm). From 2.0×1020cm-3 to 7.1×1020cm-3, the gauge factors do not change with doping concentration almost, which can be explained by tunneling piezoresistive theory. When doping concentration is low than 4.1×1019cm-3, the nonlinearities are big, and the nonlinearities become small when doping concentration is high than 4.1×1019cm-3. The nonlinearity is related to the occupied condition of trapping states in grain boundary. The longitudinal gauge factor and nonlinearity are smaller than transverse ones. Take the gauge factor and nonlinearity both into consideration, the optimal doping concentration should be 4.1×1019cm-3. The conclusions are very useful for design and fabrication of polysilicon nanofilms piezoresistive sensor.

Abstract: The polysilicon nanofilms have significant piezoresistive characteristics. In this paper, an analysis of tunneling piezoresistive effect of p-type polysilicon nanofilms is presented based on the experimental data. The analysis results show that the tunneling piezoresistive effect is much remarkable than piezoresistive effect of neutral region, and the former is about 1.3 to 1.5 times of the latter. The higher is doping concentration, the more remarkable tunneling piezoresistive effect is. This advantage can be utilized to improve the temperature characteristics of polysilicon piezoresistive sensor.

Abstract: This work reports on strength behaviour of polysilicon thin film flexure hinge. In order to develop a microscopic modelling of thin film flexure hinge for microstructures, in situ test benches have been designed and fabricated. The experiment demonstrated that a deviation between the macroscopic theory value and experimental result. A model similar to that used for rotational stiffness in macroscopic steel is used to fit testing data for polysilicon film flexure hinge. The dynamic characteristic and fatigue behaviour of the thin film flexure hinge were also investigated. The hinge was excited by an integrated electro-thermal microactuator that could be self-heated and driven. Resonant frequency of the polysilicon flexure hinge test benches is 6.5 Hz, and the maximum operating frequency reached 1KHz. When a cyclic loading of 1μN.μm was exerted to the micromachining flexure hinge, the limit stress alternation number exceed 1.0×108. When the stress alternation number exceeded 1.0×109, the polysilicon beam of microactuator would lost its elastic character. If the micro hinge operated at high temperature (exceed 200/), the lifetime would decreased. If the working temperature were too high, the micro hinge would be burned out.

Abstract: A new approach to grain boundary engineering for photovoltaic polysilicon has been attempted using a new processing method of unidirectional and rotational solidification from the melt, in order to control the grain boundary microstructure and to produce desirable bulk electrical properties. The effect of grain boundary microstructure on bulk electrical properties of polysilicon can be more precisely evaluated by introducing a new parameter “directional grain boundary density (DGBD)” in connection with basic knowledge of structure-dependent grain boundary electrical properties, the grain boundary character distribution (GBCD) and grain boundary geometrical configuration which can be experimentally determined by Orientation Imaging Microscopy (OIM). We report the usefulness of this approach to development of high performance polysilicon.

Abstract: The formation and growth mechanism of polysilicon grains in thin films via laser annealing of amorphous silicon thin films are studied. The complete understanding of the mechanism is crucial to improve the thin film transistors used as switches in the active matrix liquid crystal displays. To understand the recrystallization mechanism, the temperature history and liquidsolid interface motion during the excimer laser annealing of 50-nm thick amorphous and polysilicon films on fused quartz substrates are intensively investigated via in-situ time-resolved thermal emission measurements, optical reflectance and transmittance measurements at near infrared wavelengths. The front transmissivity and reflectivity are measured to obtain the emissivity at the 1.52 μm wavelength of the probe IRHeNe laser to improve the accuracy of the temperature measurement. The melting point of amorphous silicon is higher than that of crystalline silicon of 1685 K by 100-150 K. This is the first direct measurement of the melting temperature of amorphous silicon thin films. It is found that melting of polysilicon occurs close to the melting point of crystalline silicon. Also the optical properties such as reflectance and transmittance are used to determine the melt duration by the detecting the difference of the optical properties of liquid silicon and solid silicon.