850 µm500 µmSiliconNitrideUniversity of California at BerkeleyCollege of EngineeringEECS C245 – ME C218 Midterm ExamScorePointsPossibleScoreTotalDIMPLE depth 0.75 µmUniversity of California at BerkeleyCollege of EngineeringEECS C245 – ME C218 Midterm ExamFall 2003 Prof. Roger T. Howe October 15, 2003Dr. Thara Srinivasan Your name: ______________________________ Circle your course: EE C245 ME C218 Your student ID: ________________________GuidelinesClosed book and notes; two 8.5” x 11” pages (both sides) of your own notes are allowed. You may use a calculator.Do not unstaple the exam.Show all your work and reasoning on the exam in order to receive full or partial credit.ScoreProblem PointsPossible Score 1 8 2 12 3 12 4 12 5 12 Total 5611. Microfabrication and Miniaturization [8 pts.]Answer the following questions:a. [2 pts.] Of the following etching methods, circle the one which could beused to create deep trenches with vertical sidewalls on a Si {100} wafer:KOH DRIE sputtering XeF2 b. [2 pts.] For each the following materials, list one method which can beused to deposit or apply a thin film onto a Si wafer: polysilicon aluminum photoresist PSG___________ ___________ ___________ __________c. [2 pts.] When doing the layout of a spring suspension for a MEMSaccelerometer, you want to compare how much the beams will sag undertheir own weight for different dimensions. You begin by looking at howthe gravitational force scales as the system is miniaturized, and find thatgravitational force scales as [sx], where s is the length scale and x = 1 2 3 4 d. [2 pts.] Draw the (111) plane and the [110] direction on the axes below.2xyz2. Bulk Etching [12 pts.]The Si {100} wafer shown below has a patterned silicon nitride mask on its topsurface, and an unpatterned nitride layer on the bottom surface. With TMAH, the etchselectivity between the {100} and {111} planes is 35:1, and the {100} etch rate is 1µm/min. Assuming that the nitride layer and all other Si crystal planes are not etched, sketchthe wafer cross section after 400 minutes of etching on the drawing at the bottom ofthe page. Also enter the following dimensions after etching:a. Si etch depth [2 pts.] ____________b. Si etch width at top [3 pts.] ____________c. Si etch width at bottom [3 pts.] ____________ 3A’SiliconNitride850 µm500 µmAd. [4 pts.] Sketch the cross section after 400 minutes of etching.3. Surface Micromachining [12 pts] The layout of the lateral resonator shown below is sent to the MUMPS foundry to befabricated. The MUMPS film thicknesses are:Silicon nitride 0.6 µmPOLY0 0.5 µmDIMPLE depth 0.75 µmOxide1 2 µmPOLY1 2 µmThe order in which the masks are used is as follows:POLY0DIMPLEOxide1POLY14ANCHOR1DIMPLEPOLY1POLY0AA’Draw the following cross sections (A-A’) on the substrates given below using the provided guide lines:a) [6 pts.] After the process has reached the Oxide1 etching for ANCHOR1 but before photoresist removal: b) [6 pts.] Before release: 5Silicon substrate Silicon substrate (extra in case you need it)Silicon substrate AA’6Silicon substrate (extra in case you need it)4. MEMS suspension analysis [12 points](a) [3 pts.] What is the numerical value of the spring constant kx (units: N/m) of the simple one-sided suspension on the left? Given: polysilicon structural material with E = 160 GPa. In case it’s not on one of your formula sheets, the spring constant of a cantilever of length Lc, width W, and bending thickness h is given by 334cxLEWhk .(b) [3 pts.] What is the numerical value of the spring constant kx (units: N/m) of the folded one-sided suspension on the right?7(c) [3 pts.] You’re unsatisfied with these designs, so you turn to a double-folded, one-sided suspension. What is the numerical spring constant kx (units: N/m) of this suspension?(d) [3 pts.] What is the resonant frequency in kHz of the lateral resonator with the simpleone-sided suspension from part (a)? Given: the density of polysilicon is 2330 kg/m3 and the area of the shuttle and comb fingers is 700 m2; you can neglect the effective mass of the suspension beams.85. Electrostatic Actuators [12 points](a) [4 pts.] The lower electrode is connected to a voltage supply of value V = 2 V, while the suspended plate is grounded. The gap between the lower electrode and the plate isgo = 1 m. Find the area A of the lower electrode in m2 such that the electrostatic force on the plate is 100 nN. (b) [4 pts.] What is the electrical spring constant ke in N/m for the applied voltage and lower electrode area you found in part (a)? If you were unable to solve part (a), you can use A = 4000 m2 for this part.9In a different structure, we would like to use levitation electrodes around the perimeter of the suspended plate to apply vertical force in the z direction to the plate. The capacitancevariation for one electrode (shown in cross section above) is found by finite-element analysis and plotted on the graph below. (c) [4 pts.] For a voltage Vf = 5 V, find the levitation force in nN, given that the vertical position of the plate is z =
View Full Document
Unlocking...