The RF PIN diode as we know it today was invented by J. Nishizawa in 1950. Now, almost 70 years later, a new PIN diode concept—shielded-anode PIN diode (SAPIN)—has emerged. This new PIN diode offers 10 to 50 times better “OFF” isolation thanks to the introduction of a simple electrostatic shield. An “OFF” isolation greater than 40 dB at 2 GHz and 0 Vdc is achieved from a single series device. The theory of operation will be presented here along with measurements on fabricated silicon (Si) SAPIN didoes.
PIN Diode Operation
A PIN diode is built with a wide undoped intrinsic (i-region) semiconductor, usually Si or gallium arsenide (GaAs). The i-region is sandwiched between the p+ anode and the n+ cathode. Both are connected to a conducting metal like gold or aluminum (Fig. 1).