D with the results obtained in part c discuss which

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d) With the results obtained in part c, discuss which method is easier to detect the changes. Problem 4 MEMS Processing (Previous Exam question) The following brief description is taken from a MEMS textbook :
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2 “Doer ing, et al. demonstrated a thermal bimorph cantilever that combined the use of the Coanda effect with forced convection, to allow a laminar flow to be steered into one of two outlet ports under electrical control (see figure at left). They used an electro-chemical etch-stop and plasma etch edge release to form 11 m thick n-epitaxial cantilevers that included a p++ boron diffusion for heating resistors and an 11 m aluminum layer to form the bimorph with silicon (see cross section at right figure).” Principle of a thermal bimorph cantilever directing fluid flow into one of two outlets [Background information- The n+ contact for etch stop is an n+ island fabricated on the n-type epitaxial Si. By applying a voltage at the n+ contact during KOH etch of the p-type substrate, etching rate will stop at the pn boundary.] (a) To aid your understanding of how this device operates, draw a top-view of the device. Label all important boundaries. (b) When the p++ resistor pattern is heated up by resistive heating, will the cantilever structure curve upward or downward? Briefly explain. (c ) Starting with a p-type Si wafer with an n-type epitaxially grown Si, design a process flow to fabricate the bimorph device. Describe the process steps in the left column and sketch the cross-sections in the right column PROCESS DESCRIPTION CROSS-SECTIONS Problem 5 MEMS-before-IC Process The following cross-section shows a poly-Si MEMS integrated with CMOS devices. The CMOS uses a p- well inside the n-type epitaxial layer. For simplicity, only the NMOS transistor is shown [the PMOS transistor fabricated on the n-type epi layer is not shown explicitly]. Al is used as Metal-1. Start with the epitaxial layer on Si substrate, design a process flow to fabricate this microsystem. Show cross-sections at major process steps.
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