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,
$R_{C}$
, of 0.25
$\text{m}\Omega \cdot $
cm
²
and an OFF capacitance,
$C_{\mathrm{\scriptscriptstyle OFF}}$
, of 17.5 nF/cm
²
, the diodes have an RF figure of merit
$F_{\mathrm {oc}} =$
(
$2\pi R_{C}\,\,C_{\mathrm{\scriptscriptstyle OFF}})^{-1}$
of 36.5 GHz. The RF model suggests that reducing
$R_{C}$
to less than
$5\times 10^{-5} \Omega \cdot $
cm
²
will 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.