$-$Both the mask layers ANCHOR$2$ and P$2$P$1$VIA instruct the PolyMEMS foundry to etch Oxide$2.$ This may seem unnecessary and inefficient. Explain why it makes sense $($a$)$ to have two different mask layers for this etch in your CAD layout, and $($b$)$ to actually have two different lithography and etching steps.

$-$One may be tempted to put Metal on top of Poly$1,$ but this is not possible in the PolyMEMS process. Explain what would happen if you attempted to do that, $($a$)$ by using the mask layers POLY$1$ and METAL, $($b$)$ by using the mask layers POLY$1,$ P$2$P$1$VIA, and METAL. Draw a cross section for each case to illustrate.$$

$-$An occasional complaint about the PolyMEMS process is that all structural materials $($polySi$,$ gold$)$ are conducting. Therefore, it is not possible to create a released structure with electrically isolated regions $($which would be useful, e$.$g$.,$ for controlling an actuator with multiple degrees of freedom$).$ Let's modify the PolyMEMS process to fix this issue and add another structural layer between Poly$1$ and Poly$2,$ which we will call "Insulator".

$-$ Propose a material for "Insulator" and explain why you made this choice.

$-$ What new mask layers do you need for this modified PolyMEMS process? Certainly you will need an INSULATOR mask. Do you need any other masks?

$-$ Describe the modified process flow. Specifically, list the updated processing steps between the Poly$1$ deposition and the Poly$2$ deposition. As a reminder, the original processing sequence was:

Deposit Poly$1$ Lithography with POLY$1$ mask and polySi etch Deposit Oxide$2$ Lithography with P$2$P$1$VIA mask and oxide etch Lithography with ANCHOR$2$ mask and oxide etch Deposit Poly$2$

$-$ Based on your modified process, draw the layout $($top view$)$ and a cross section of a released structure that has electrically isolated regions.