A thermal bimorph can be used as an actuator. In this problem, you will use the principles of “crayon engineering” to design a process and mask set that will produce a silicon‐based cantilever thermal bimorph with an integrated heater and an underlying hole structure as shown below. (Silicon‐based means that the final structure is made of silicon, plus oxide, nitride, and metal as needed. You don’t have to use a plain silicon wafer, but you can’t make the whole thing out of a completely different material like metal or SU8.) A description of the structure follows; a top view is shown in Figure 2. Where a dimension is not specified (like the lateral extent of the hole), you are free to choose a process that you think makes sense. This may turn out to be an economic trade‐off (for example, cost of processes vs. wasted space on the wafer). Cantilever composition: The cantilever includes a silicon structure, a metal layer on top of that (you can choose either Al or Au), an integrated heater to actuate the bimorph, and either nitride or oxide layer(s) to keep the heater from shorting out to the bimorph. The order of the layers is not specified up front; you can pick any order that is buildable. Silicon cantilever: 100 microns long, 20 microns wide, and 1.5 micron thick Metal layer: 0.5 microns thick and covers the whole top surface of the cantilever, to within process biases. Underlying hole: at least 10 microns deep. Integrated heater: 0.5 microns thick, made of doped polysilicon. Make sure that the heater has an accessible contact pad.             When we do crayon engineering, it is useful to identify the challenges of the process flow (those points where we must be particularly careful to obey the laws of physics) early on. Examples could include thermal compatibility, chemical compatibility, and the ability to pattern the device geometry. Identify what you see as the major challenges for this process (a few words each). Pick three, and explain why they are an issue. Brainstorm three different ways of approaching the process, and explain them briefly. You don’t have to have all of the details ironed out on these Choose one approach and flesh it out. You need to sketch the mask set with key dimensional relations and write out the steps of the process flow. Specify materials and the proposed deposition and etch methods, and be sure to include as steps in your process the required wafer cleans, application of photoresist, and stripping of photoresist. If a dimension on the mask affects the success of the process, make sure you specify it. Be sure to show cross‐sectional and planar views of all key steps in the process.