Input Capacitance in MOSFET
Input capacitance is an important parameter in MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) devices as it affects the overall performance and speed of the transistor. It is the capacitance that needs to be charged or discharged during the switching operation of the transistor.

Components of Input Capacitance
The input capacitance of a MOSFET can be divided into several components, including:

1. Gate Diffusion Capacitance:
The gate diffusion capacitance (Cgd) is the capacitance between the gate and the diffused regions in the MOSFET structure. It is formed due to the overlap between the gate electrode and the source/drain diffusion regions. This capacitance is dependent on the geometry and doping profile of the device.

2. Gate Parasitic Capacitance:
The gate parasitic capacitance (Cgp) is the capacitance between the gate and the substrate or the surrounding structures in the MOSFET. It includes the capacitance between the gate and the bulk silicon, as well as any capacitance between the gate and the adjacent conductive structures. This capacitance is mainly determined by the device layout and the dielectric properties.

3. Gate Oxide Capacitance:
The gate oxide capacitance (Cox) is the capacitance between the gate and the oxide layer in the MOSFET. It is the dominant component of the input capacitance in most cases. The gate oxide capacitance is directly related to the physical thickness and dielectric constant of the gate oxide.

Dominant Component
Among the given options, the gate oxide capacitance (Cox) is the dominant component in the input capacitance of a MOSFET. This is because the gate oxide capacitance is directly related to the physical thickness and dielectric constant of the gate oxide, which are the major factors affecting the capacitance.

The gate diffusion capacitance (Cgd) and gate parasitic capacitance (Cgp) also contribute to the input capacitance but their impact is usually smaller compared to the gate oxide capacitance. These capacitances can be minimized through device optimization and layout techniques.

Therefore, the correct answer is option 'C' - Gate oxide capacitance.