RF Characterization of Diamond Schottky p-i-n Diodes for Receiver Protector Applications

Diamond Schottky p-i-n diodes have been grown by plasma-enhanced chemical vapor deposition (PECVD) and incorporated as a shunt element within coplanar striplines for RF characterization. The p-i-n diodes have a thin, lightly doped n-type layer that is fully depleted by the top metal contact, and they operate as high-speed Schottky rectifiers. Measurements from dc to 25 GHz confirm that the diodes can be modeled by a voltage-dependent resistor in parallel with a fixed-value capacitor. In the OFF state with a dc bias of 0 V, the diode insertion loss is less than 0.3 dB at 1 GHz and increases to 14 dB when forward biased to 7.6 V. With a contact resistance, RC, of 0.25 mΩ·cm2and an OFF capacitance, COFF, of 17.5 nF/cm2, the diodes have an RF figure of merit Foc= (2π RCCOFF)-1of 36.5 GHz. The RF model suggests that reducing RCto less than 5 × 10-5Ω·cm2will enable input power rejection exceeding 30 dB. Compared to conventional silicon or compound semiconductor based power limiters, the superior thermal conductivity of the diamond Schottky p-i-n diodes makes them ideally suitable for RF receiver protectors (RPs) that require high power handing capability.