N-well resistance modelling in Q-factor of doughnut-shaped PN varactors

• The N-well resistance in doughnut-shaped PN varactors is physically modelled.
• Our model incorporates internal geometrical parameters and a number of basic cells.
• The model, numerically validated, adequately predicts the bias voltage dependence.
• Parasitic components and proximity effects are considered for the modelled Q-factor.
• Accounting for N-well resistances, Q-factors are accurately predicted up to 10 GHz.

In this paper the N-well resistance in doughnut-shaped PN varactors, with the cathode connected to an N+ buried layer, has been modelled. The proposed expression for the N-well resistance, numerically validated, is based on the device geometry and overlapping of adjacent basic cells, and adequately reproduces its applied reverse bias voltage dependency. Once the varactor extrinsic parasitic components are extracted considering proximity effects, from anode-to-cathode measured RF admittances, and frequencies ranging from 0.5 GHz to 10 GHz, the impact of the N-well resistance on the experimental varactor quality factor is determined for reverse biases up to 5 V.