Sherif Sedky

Characterization and optimization of infrared poly SiGe bolometers

In this paper, we present a complete characterization of poly SiGe bolometers. Devices having different dimensions and different geometry have been fabricated. The dependence of the low-frequency noise and of the temperature coefficient of resistance (TCR) on resistivity in poly SiGe has been measured and modeled. The impact of resistivity, bias voltage, thermal conductance, thickness, and dimensions of the active element on the device performance has been investigated. It has been demonstrated that, by using the appropriate absorber and by optimizing the device parameters, poly SiGe bolometers are suitable for realizing high-performance focal plane arrays (FPAs).

Thermoelectric MEMS generators as a power supply for a body area network

Miniaturized and cost-effective thermoelectric generators (TEG) scavenging energy from environment could potentially provide power autonomy to consumer electronic products operating at low power. For example, TEG mounted in a wristwatch have been used to generate electricity from human heat. The key point of IMECs research in this field is the realization of a body area network, consisting of a set of wireless sensors/actuators, able to provide health, sports, comfort, and safety monitoring functions to the user. The development of miniature energy scavengers built on MEMS technology is a primary goal of the ongoing research, as this will make the network truly power autonomous. In this paper, the modeling and a novel design of MEMS TEG especially conceived for human body applications are described. The design is built on the basis of a thermal model of the device, which includes the human body as one of its important elements. For this purpose, the research on human body thermal features is performed. The TEG prototype made with commercial thermopiles is tested with power conditioning electronics and a wireless module mounted on a watchstrap.

Experimental determination of the maximum post-process annealing temperature for standard CMOS wafers

This paper reports on the experimental determination of the maximum post-process annealing temperature for standard 0.35 /spl mu/m CMOS wafers with aluminum based interconnections and tungsten plugs, without introducing significant modifications to their standard characteristics. The impact of increasing the post-processing temperature from 475/spl deg/C to 575/spl deg/C, for periods varying between 30 and 90 min, on both the front and back end is analyzed. 0.35 /spl mu/m CMOS technologies with different Al alloys, Al-1wt%Si-0.5wt%Cu (AlSiCu) or Al-0.5wt%Cu (AlCu), and different back end structures are considered. It is illustrated that the maximum annealing temperature is a function of the structure and composition of the interconnection layers and their maximum allowable resistance increase. It is also demonstrated that the transistor characteristics, the silicide quality and the leakage currents are as good as unaffected by annealing for 90 min at temperatures up to 525/spl deg/C.

IR bolometers made of polycrystalline silicon germanium

Abstract This paper reports the first fabrication of surface-micromachined microbolometers made of polycrystalline silicon-germanium alloy (poly Si 0.7 Ge 0.3 ). The electrical and mechanical properties of this material have been measured and the effects of the deposition conditions and annealing temperature on them have also been investigated. The complete process for the bolometer fabrication is presented and the possibility of reducing the process temperature to 650 °C is demonstrated. The thermal behaviour of the device is fully analysed and it is demonstrated that the use of poly Si 0.7 Ge 0.3 instead of polycrystalline Si (poly Si) decreases the thermal conductance of the device (values lower than 10 −6 W K −1 are obtained). Preliminary measurements give a value of 10 4 V W −1 for the IR responsivity.

Structural and mechanical properties of polycrystalline silicon germanium for micromachining applications

In this paper, we propose polycrystalline silicon germanium (poly SiGe) as a material suitable for MEMS applications. Films are prepared by chemical vapor deposition (CVD) at atmospheric pressure (AP) or reduced pressure (RP). The structure of the films is investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for different deposition and annealing conditions. The stress in the as-grown and annealed layers is measured, and the correlation between stress and structural properties is discussed. It is demonstrated that by adjusting the deposition conditions, the stress of the as-grown material can be varied from -145 to 60 MPa. Examples of poly SiGe micromachined devices, prepared at 650/spl deg/C, are presented. It is shown that by using as-grown poly SiGe, it is possible to realize surface-micromachined suspended membranes having 0.6-/spl mu/m-wide and 50-/spl mu/m-long supports. The effect of the average stress and stress gradient on the mechanical stability of surface-micromachined structures is illustrated. Finally, the strain in poly SiGe is measured, and it is found to vary, according to the deposition conditions from -6.88/spl times/10/sup -4/ to 3.6/spl times/10/sup -1/ These values are compared to those measured for APCVD poly Si.

Nonlinear Dynamics of Spring Softening and Hardening in Folded-MEMS Comb Drive Resonators

This paper studies analytically and numerically the spring softening and hardening phenomena that occur in electrostatically actuated microelectromechanical systems comb drive resonators utilizing folded suspension beams. An analytical expression for the electrostatic force generated between the combs of the rotor and the stator is derived and takes into account both the transverse and longitudinal capacitances present. After formulating the problem, the resulting stiff differential equations are solved analytically using the method of multiple scales, and a closed-form solution is obtained. Furthermore, the nonlinear boundary value problem that describes the dynamics of inextensional spring beams is solved using straightforward perturbation to obtain the linear and nonlinear spring constants of the beam. The analytical solution is verified numerically using a Matlab/Simulink environment, and the results from both analyses exhibit excellent agreement. Stability analysis based on phase plane trajectory is also presented and fully explains previously reported empirical results that lacked sufficient theoretical description. Finally, the proposed solutions are, once again, verified with previously published measurement results. The closed-form solutions provided are easy to apply and enable predicting the actual behavior of resonators and gyroscopes with similar structures.

Pulsed-laser annealing, a low-thermal-budget technique for eliminating stress gradient in poly-SiGe MEMS structures

In this paper, we demonstrate eliminating the stress gradient in polycrystalline silicon germanium films at temperatures compatible with standard CMOS (Al interconnects) backend processing. First, we study the effect of varying the germanium concentration from 40% to 90%, layer thickness, deposition pressure from 650 to 800 mtorr and deposition temperature from 400 to 450/spl deg/C, on the mechanical properties of SiGe films. Then the effect of excimer laser annealing (248 nm, 38 ns, 780 mJ/cm/sup 2/) on stress gradient is analyzed. It is demonstrated that stress gradient can be eliminated completely by depositing Si/sub x/Ge/sub 1-x/(10%<x<92%) bilayers, with the bottom film exposed to a single laser pulse, which changes the grain microstructure of both the bottom and top films. Furthermore, laser annealing seems to reduce surface roughness, significantly, which is an attractive feature for some MEMS applications.

Generation of approximate focus-wave-mode pulses from wide-band dynamic Gaussian apertures

It is demonstrated that an approximation to the focus-wave-mode field can be generated from a dynamic Gaussian aperture. A source of this type is characterized by the time variation of its effective radius. The performance of such an aperture is studied in detail; it is demonstrated that the dynamic aperture shows a great enhancement over the corresponding static one. The types of source investigated provide an efficient scheme to launch narrow Gaussian pulses from extended apertures.

Recent progress in modularly integrated MEMS technologies

Various approaches to post-CMOS, monolithic integration of MEMS with electronics are described. In particular, recent progress toward a high-performance, low-process-temperature MEMS technology based on polycrystalline silicon-germanium (poly-SiGe) is presented.

New low-stress PECVD poly-SiGe Layers for MEMS

Thick poly-SiGe layers, deposited by plasma-enhanced chemical vapor deposition (PECVD), are very promising structural layers for use in microaccelerometers, microgyroscopes or for thin-film encapsulation, especially for applications where the thermal budget is limited. In this work it is shown for the first time that these layers are an attractive alternative to low-pressure CVD (LPCVD) poly-Si or poly-SiGe because of their high growth rate (100-200 nm/min) and low deposition temperature (520/spl deg/C-590/spl deg/C). The combination of both of these features is impossible to achieve with either LPCVD SiGe (2-30 nm/min growth rate) or LPCVD poly-Si (annealing temperature higher than 900/spl deg/C to achieve structural layer having low tensile stress). Additional advantages are that no nucleation layer is needed (deposition directly on SiO/sub 2/ is possible) and that the as-deposited layers are polycrystalline. No stress or dopant activation anneal of the structural layer is needed since in situ phosphorus doping gives an as-deposited tensile stress down to 20 MPa, and a resistivity of 10 m/spl Omega/-cm to 30 m/spl Omega/-cm. With in situ boron doping, resistivities down to 0.6 m/spl Omega/-cm are possible. The use of these films as an encapsulation layer above an accelerometer is shown.