4.1.1.2 Contributions to ${\it C}_{\mathrm{gd}}$

The gate drain capacitance ${\it C}_{\mathrm{gd}}$ is written as:

$${\it C}_{\mathrm{gd}} ({\it V}_{\mathrm{DS}}) = C_\mathrm {met} + C_\mathrm {pass}+ C_\mathrm {semi}({\it V}_{\mathrm{DS}})$$ (4.5)

as was suggested in [65]. The first two contributions are independent of ${\it V}_{\mathrm{DS}}$  representing the contributions of the gate and drain metal periphery (C $_\mathrm {met}$) and the coupling of the gate metal with the semiconductor caps through the SiN passivation (C $_\mathrm {pass}$). The ${\it V}_{\mathrm{DS}}$  dependence of ${\it C}_{\mathrm{gd}}$  arises mostly from the coupling of gate and drain through the barrier and channel layer, represented by C $_\mathrm {semi}$.