Based on the source material, formulate comprehensive answers to the following prompts.

1. Compare and contrast the four VLSI design styles presented in the text: FPGA, Gate Array, Standard-Cell Based, and Full Custom. Analyze the trade-offs between them regarding prototyping time, manufacturing process, cost, and design flexibility.
2. Describe the complete VLSI IC circuits design flow, starting from specifications and ending with the physical layout. For each major step (Behavioral description, RTL description, Logic synthesis), explain its purpose and the type of description it produces.
3. Detail the physical structure of a MOSFET as described in the text. Explain the role of the metal gate, the insulating oxide layer, and the semiconductor substrate, and how these components form a capacitor-like structure.
4. Explain the operation of a depletion-load nMOS inverter. Contrast its advantages and disadvantages with enhancement-load nMOS inverters and the static CMOS inverter.
5. Describe how sequential circuits like SR latches are implemented in CMOS technology using both NOR and NAND gates. Explain the different states (Set, Reset, Hold) and the input conditions required to achieve them for each implementation.