In this research, the degradation effect of the low temperature polycrystalline silicon TFTs (LTPS TFTs) under dynamic stress was investigated. The experiment results revealed that the degenerate behaviors of n- and p-type poly-Si were different. In p-channel TFT, it was observed that the degradation of threshold-voltage (Vth) was closely associated with the stress frequency of ac stress. The degradation was more serious at low-frequency stress than that at high-frequency stress. The degradation of electrical characteristics of device is mainly dominated by the self-heating enhanced negative bias temperature instability effect. Moreover, the increased temperature around the environment could make the degradation of characteristics more serious, such as Vth shift (fixed charge), degraded S.S (dangling bonds). We suggest that the generation of deep states originated from bond broken at both of grain-boundary and interface state was explained the degradation mechanism of threshold-voltage. In n-channel TFT, the degradation characteristics may be attributed to both of the temperature effect and the hot carrier effect under the different stress frequency. At low-frequency stress, Vth shift (positively) and mobility are increased after 100 seconds stress because of the temperature effect. However, Vth shift (negatively) and mobility are decreased after 500 seconds stress because of the effect of the state creation near the drain regime. At high-frequency stress, the times of the switch is numerous, and result in the on-state current decreased because of the trap state generated.

On-chip characterization devices have been used to extract the Young’s modulus, average stress and stress gradient of polysilicon doped with phosphorus using thermal diffusion. Devices for extracting the Young’s modulus, average stress and stress gradients have been designed to work within the range of expected material property values. A customized fabrication process was developed and the devices were fabricated. Static and resonant tests were performed using clamped-clamped and cantilever beams in order to extract material properties. The experimental setup and detailed experimental results and analysis are outlined within. Several doping concentrations have been studied and it has been concluded that the Young’s modulus of polysilicon doped for 2 hours increases by approximately 50GPa and the average stress of polysilicon doped for 2.5 hours becomes more tensile by approximately 63 MPa. It has also been found that short doping times can introduce a large enough stress gradient to create a concave up curvature in free-standing structures. This work was performed in order to determine the usability of doping as a means to increase the sensitivity of temperature and pressure sensors for harsh environments. It has been concluded that doping is a promising technique and is worth studying further for this purpose.

The development of microscale and nanoscale devices has outpaced the development of metrology tools necessary for their complete characterization. In the area of thermal MEMS technology, accurate measurements across a broad range of temperatures with high spatial resolution are not trivial. Thermal MEMS are devices in which the control and manipulation of temperature is necessary to perform a desired function, and are used in actuation, chemical sensing, nanolithography, thermal data storage, biological reactions and power generation. In order to properly design for reliability and performance issues amongst these devices and verify modeling accuracy, the temperature distribution under device operating conditions must be experimentally determined. Raman spectroscopy provides absolute temperature measurements with spatial scales below 1 micron, which is sufficient for most MEMS devices. In this work, a detailed study of Raman spectroscopy as an optical thermal metrology tool was performed. It is shown that a calibration of the Stokes shift with temperature yields a linear calibration for measurements up to 1000?n polysilicon. These coefficients were determined for polysilicon processed under various conditions (575-620?B and P doping) to assess the effects of microstructural variations on Raman spectra. The Stokes peak was also shown to shift linearly with an applied pure bending stress. In order to make stress-independent thermometry measurements, the ratio of the Stokes to anti-Stokes signal intensities and the Stokes linewidth were calibrated over the same temperature range. Using the calibration data, Raman spectroscopy was implemented for the evaluation of temperature of thermal MEMS. Heated AFM cantilevers and micro-beam heaters were chosen due to their wide range of applications. Different thermal and mechanical boundary conditions were considered by studying both the beams and cantilevers, resulting in varying levels of thermal stress. By using the three calibrations in a complementary fashion, the validity of Raman thermometry was explored. Device temperatures of up to 650?nd their corresponding uncertainties were found, and used to verify FEA modeling. Effects of thermally induced stresses were taken into account and analyzed. Possible uncertainties such as laser heating, spatial and spectral resolution, light collection efficiency, measurement uncertainty, and instrumental drift were reported and elucidated.

Silicon based on-chip optical phased arrays are an enabling technology to achieving agile and compact large angle beam steering. In this work, a single layer array is presented, and approaches to multilayer 3D photonic integration for achieving a 2D array are also discussed. Finally, two dimensional optical beam steering is achieved using both thermo-optic and wavelength tuning. Various structures are considered as an alternative to the conventionally used shallow etched surface gratings to achieve narrow beam widths in the far field along with low switching power. The corrugated waveguide interspersed with 2D photonic crystal for crosstalk suppression is presented as a novel structure for coupling to free space that can provide lithographically defined index contrast in a single fabrication step, along with the smallest beam widths presented to date, at 0.25°. In addition, a polysilicon overlay with an oxide etch stop layer on top of a silicon waveguide is also presented as a grating coupler that achieves narrow far field beam widths. With this structure, two dimensional steering of 20° X 15° is demonstrated with a 16 element optical phased array, with a beam width of 1.2° X 0.4° and maximum power consumption of 20mW per channel. / text

The heteroepitaxial growth of cubic silicon carbide (3C-SiC) on (111) silicon (Si) substrates, via a horizontal hot-wall chemical vapor deposition (CVD) reactor, has been achieved. Growth was conducted using a two step process: first the Si substrate surface is converted to SiC via a carbonization process and second the growth of 3C-SiC is performed on the initial carbonized layer. During carbonization, the surface of the Si is converted to 3C-SiC, which helps to minimize the stress in the growing crystal. Propane (C3H8) and silane (SiH4), diluted in hydrogen (H2), were used as the carbon and silicon source, respectively. A deposition rate of approximately 10 µm/h was established during the initial process at a temperature of ~1380 °C. The optimized process produced films with X-ray rocking curve full-width at half-maximum (FWHM) values of 219 arcsec, which is significantly better than any other published results in the literature. Once this process was developed a lower temperature process was developed at a slower growth rate of ~2 µm/h at 1225 °C. The crystal quality was inferior at the reduced temperature but this new process allows for the growth of 3C-SiC(111) films on oxide release layers for MEMS applications. In addition, for electronic device applications, a lower temperature process reduces the generation of defects caused by the nearly 8 % mismatch in the coefficient of thermal expansion (CTE) between 3C-SiC and Si. Finally a new process using a poly-Si seed layer deposited on an oxide-coated Si wafer was used to form 3C-SiC films for MEMS applications. The results indicated initially that the films may even be monocrystalline (based on X-ray evaluation) but later analysis performed using TEM indicated they were highly-ordered polycrystalline films. The grown 3C-SiC films were analyzed using a variety of characterization techniques. The thickness of the films was assessed through Fourier Transform infrared (FTIR) spectroscopy, and confirmed (in the case of growth on poly-Si seed layers) by cross-section scanning electron microscopy (SEM). The SEM cross-sections were also used to investigate the 3C-SiC/oxide interface. The surface morphology of the films was inspected via Nomarsky interference optical microscopy, atomic force microscopy (AFM), and SEM. The crystalline quality of the films was determined through X-ray diffraction (XRD).

Les progrès technologiques de ces dernières années ont permis une très forte intégration des composants de la microélectronique à l'échelle nanométrique. Face aux limites de la miniaturisation classique, les technologies d'intégration en trois dimensions (3D) ouvrent la voie vers des dispositifs miniaturisés hétérogènes avec de nouvelles générations de puces. En parallèle, de nouveaux concepts tels que les nanofils sans jonction et les nanofils en silicium polycristallins permettent à terme d'imaginer des procédés froids et des dispositifs à faible coût permettant une intégration 3D hyperdense sur un CMOS stabilisé. La fabrication de NEMS à base de nanofils polycristallins pour la détection de masse sur CMOS est donc une nouvelle opportunité « More-Than-Moore ». Les capteurs pourraient être disposés en réseau dense en s'inspirant des architectures mémoires et imageurs. L'adressage individuel de chaque NEMS, la possibilité de les fonctionnaliser à la détection de molécules particulières, et la multiplication des capteurs sur une grande surface (« Very Large Integration » (VLSI)) permettraient la mise en œuvre d'un nouveau genre de capteur multi-physique, compact et ultrasensible. Le but de ces travaux de thèse a donc été la fabrication et l'évaluation des performances de NEMS à base de nanofils en poly-silicium. L'enjeu fut de trouver des procédés avec un budget thermique compatible à une intégration sur back-end. Une étude rigoureuse sur les propriétés physico-chimiques de la couche a été corrélée aux performances électriques, mécaniques, ainsi qu'au rendement des NEMS poly-Silicium, ce qui nous a permis de faire une sélection des meilleurs procédés de fabrication. Les NEMS fabriqués à basse température avec une couche active déposée à température ambiante et recristallisée par laser ont montré des performances, que ce soit au niveau de la transduction (piézorésistivité), ou de la stabilité du résonateur compétitives par rapports aux références monocristallines. / Recently, technological advances lead to a very large scale integration (VLSI) of microelectronics components at the nanoscale. Faced with the traditional miniaturization limits, the three dimensions (3D) integration open the door to heterogeneous miniaturized devices, with new chip generations. At the same time, new concepts such as junctionless nanowires and polycrystalline silicon nanowires allow to imagine low temperature processes and low-cost devices for a 3D integration on a stabilized CMOS. Poly-silicon nanowire based NEMS on CMOS for mass detection is a new "More-Than-Moore" opportunity. The NEMS could be arranged in a dense network like memory and image sensor architectures. The individual addressing of each NEMS, the functionalization for the detection of specific molecules within a large area (VLSI), allow the implementation of a new type of Multi-physics sensors, compact and highly sensitive. The purpose of this thesis has been the manufacturing and the performance evaluation of poly-silicon nanowire based NEMS. The challenge was to find the best processes with a back-end compatible thermal budget. A rigorous study of the layer physicochemical properties has been correlated with the electrical, mechanical performances and the yield of poly-silicon NEMS. This allowed us to make a selection of the best fabrication processes. NEMS manufactured at very low temperature with an active layer deposited at room temperature and recrystallized by a laser annealing exhibited high performances in terms of transduction (piezoresistivity) and frequency stability comparable to monocrystalline references. Polycrystalline silicon.

In this dissertation, advances in the fields of Photonics, and Plasmonics, and specifically, single cell analysis and waveguide sensing will be addressed. The first part of the dissertation is on Finite Difference Time Domain (FDTD) optimization and experimental demonstration of a nano-scale instrument that allows sensing at the cellular and subcellular levels. A new design of plasmonic coupler into a nanoscale waveguide is proposed and optimized using FDTD simulations. Following this, a subcellular nanoendoscope that can locally excite fluorescence in labelled cell organelles and collect the emitted fluorescent light for detailed spectrum analysis is fabricated and tested. The nanoendoscope has a sharp tapered tip of diameter ~ 50 nm that permits safe insertion into the cell that was confirmed by a number of viability experiments. FDTD analysis demonstrated that, with an optimized nanoendoscope taper profile, light emission and collection was very local. Thus, signal detection could be used for nano-photonic sensing of proximity of fluorophores. In further experiments, fluorescent signals were collected from individual organelles of living cells including: the nucleus of Acridine orange labelled human fibroblast cells, the nucleus of Hoechst stained live liver cells and the mitochondria of MitoTracker Red labelled MDA-MB-231 cells. In addition, this endoscope was inserted into a live organism, the nematode Caenorhabditis elegans, and in- vivo fluorescence signal was collected. Second, an innovative single step fabrication method of low loss polysilicon waveguides was developed as a potential platform for a number of photonic sensors. Optimization of a capacitively coupled plasma etching for the fabrication of a polysilicon waveguide with smooth sidewalls and low optical loss was demonstrated. A detailed experimental study on the influences of RF plasma power and chamber pressure on the roughness of the sidewalls of waveguides was conducted and waveguides were characterized using a scanning electron microscope. It was demonstrated that optimal combination of pressure (30 mTorr) and power (150 W) resulted in the smoothest sidewalls. The optical losses of the optimized waveguide were 4.1± 0.6 dB/ cm. Finally, an on-chip nanophotonic sensor for continuous blood coagulation analysis was proposed. The system was simulated using three-dimensional FDTD software. At first, the noise due to the presence of cells was calculated. Next, the design of a waveguide cladding-based filtering structure for elimination of the noise from cells was proposed and significantly decreased noise level was theoretically demonstrated.

The objective of this work is to demonstrate the feasibility of on-chip sensing of bistable mechanism state using the piezoresistive properties of polysilicon, thus eliminating the need for electrical contacts. Changes in position are detected by observing changes in resistance across the mechanism. Sensing the state of bistable mechanisms is critical in their various applications. The research in this thesis advances the modeling techniques of MEMS devices which use piezoresistivity for position sensing. A fully compliant bistable micro mechanism was designed, fabricated, and tested to demonstrate the feasibility of this sensing technique. Testing results from two fabrication processes, Fairchild's SUMMiT IV and MUMPs, are compared. The Fairchild mechanism was then integrated into various Wheatstone bridge configurations to show the advantages of bridges and to demonstrate various design layouts. Repeatable and detectable results were found with independent mechanisms and with those integrated into Wheatstone bridges. Finite element models were constructed for the different Wheatstone bridges which were used to predict piezoresistive trends. A bistable mechanism for high-acceleration sensing was designed using uncertainty analysis optimization. The piezoresistive effects for this mechanism were also modeled. Discussion concerning nonvolatile memory applications is also presented.

MEMS (MicroElectroMechanical Systems) sensors are used in acceleration, flow, pressure and force sensing applications on the micro and macro levels. Much research has focused on improving sensor precision, range, reliability, and ease of manufacture and operation. One exciting possibility for improving the capability of micro sensors lies in exploiting the piezoresistive properties of silicon, the material of choice in many MEMS fabrication processes. Piezoresistivity—the change of electrical resistance due to an applied strain—is a valuable material property of silicon due to its potential for high signal output and on-chip and feedback-control possibilities. However, successful design of piezoresistive micro sensors requires a more accurate model of the piezoresistive behavior of polycrystalline silicon. This study sought to improve the existing piezoresistive model by investigating the piezoresistive behavior of compliant polysilicon structures subjected to tensile, bending and combined loads. Experimental characterization data showed that piezoresistive sensitivity is greatest and mostly linear for silicon members subject to tensile stresses and nonlinear for beams in bending and combined stress states. The data also illustrated the failure of existing piezoresistance models to accurately account for bending and combined loads. Two MEMS force and displacement sensors, the integral piezoresistive micro-Force And Displacement Sensor (FADS) and Closed-LOop sensor (CLOO-FADS), were designed and fabricated. Although limited in its piezoresistive sensitivity and out-of-plane stability, the FADS design showed promise of future application in microactuator characterization. Similarly, the CLOO-FADS exhibited possible feedback control capability, but was limited by control circuit complexity and implementation challenges. The piezoresistive behavior exhibited by the Thermomechanical In-plane Microactuator (TIM) led to a focused effort to characterize the TIM's behavior in terms of force, displacement, actuation current and mechanism resistance. The gathered data facilitated the creation of an empirical, temperature-dependent model for the specific TIM. Based on the assumption of a nearly constant temperature for each current level, the model predicted the force and displacement for a given fractional change in resistance. Despite the success of the empirical model for the test TIM device, further investigation revealed the necessity of a calibration method to enable the model's application to other TIM devices.

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