Microelectromechanical Systems HW1

EE-446 MEMS (Microelectromechanical Systems), Spring 2018, Homework #1.

1. (15’)Use google search engine, type “MEMS applications” as key words (or any other keywords you like), perform a search on MEMS applications. Read the information you are interested. You may also refer to the paper about MEMS introduction by Brigham Young University for your reference. Then go to Youtube (http://www.youtube.com), type keywords “MEMS applications” or “what is MEMS”, perform a search, and watch the MEMS-related Youtube videos you are interested in. Based on the information you learned, list four example MEMS applications (around 1 page in total). Use your own word to briefly summarize each application. The application can be even future potential application which has not been realized now (for example, implanting MEMS micro/nano robots into human body to cure cancer, MEMS smart dust sensors, etc.). 2.(15’) Richard Feynman gave his famous lecture, “There is Plenty of Room at the Bottom,” in 1959. Read this paper and list his 10 predictions for technology in the small world. Are these predictions already realized? Just answer this question according to your understanding. It doesn’t need to be very accurate. 3.(15’) 1). List 8 categories of materials which can be used for MEMS device fabrication. Among them, what is the dominant material used for MEMS? Why is it dominant? 2). NASA is considering a MEMS pressure senor for their aerospace mission. The temperature in outer-space may be very high (>1000ºC). Apparently silicon device will fail in such high temperature. Can you suggest a material for this application? 3). During the fabrication of a MEMS humidity sensor with gold fingers on top of silicon wafer, a MEMS engineer found that the adhesion between gold (Au) and silicon surface is poor. The Au film easily peels off from Si wafer surface. Can you suggest a solution to solve the problem? 4). A MEMS company successfully made the MEMS motors. However, they found that the MEMS motors can only work for a few days and then fail. After looking into the issue, they find the reason is because the mechanical wear between the rotor and stator has led to the failure of the motor. Can you suggest a possible solution to extend the life time of the MEMS motors? 4.(15’) 1). How can we get metallurgical-grade silicon from sand? List the chemical reaction for this process. What is the purity level we can achieve for Si in this process? 2). How can we further purify metallurgical-grade silicon into electronic grade polysilicon (99.9999999% purity level)? List the two chemical reactions involved in it. 3). Silicon wafers are marked with flat(s) along the edge to differentiate its doping type and surface orientation. Decide the doping type (n or p) and surface orientation ((100) or (111)) for the following wafers according to the flats.

(a). _______________ (b). ______________ (c). _______________

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5.(15’) You need to show all intermediate steps in answering the following questions. (a). As shown in Fig. 1(a), a crystalline plane has intercepts of 1a, 2a, and 3a on the X, Y and Z axes, respectively, in which “a” is the lattice constant of cubic cell. Please find out the Miller index notation for the plane marked with gray color. (b). Determine the Miller indices for direction 1 and direction 2 in Figure 1(b). (c). Decide the intercepts of (4,1,2) plane to X, Y and Z axes, and sketch (4,1,2) plane in Figure 1(b).

Figure 1. Miller index for crystalline plane and crystalline direction

6.(25’) A bulk-micromachined MEMS accelerometer with eight-beam mass structure is shown in Figure 2. All the eight beams have the same width, length and thickness. For each beam: width Wb=620µm, length Lb=1800µm, thickness tb=10µm. For central mass: width Wm=4000µm, length Lm=4000µm, thickness tm=600µm. Young’s modulus of Si is E=170GPa, density of Si is ρ=2.33×103kg/m3. Are the eight beams connected in parallel or in series? Find displacement sensitivity (in unit of µm/g) Sd=? Resonant frequency (in unit of Hz) f0=?

Figure 2. An eight-beam mass MEMS accelerometer

(C. Du, et al., “Development of a novel accelerometer based on an overlay detection bridge, Journal of Semiconductors, 34(2), 2013.) Due on 02/06/2018, Tuesday in class.

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