A High Sensitivity, CoSi$_{2}$–Si Schottky Diode Voltage Multiplier for UHF-Band Passive RFID Tag Chips

Abstract

A ultra high frequency (UHF)-band high sensitivity voltage multiplier was designed based on Cobalt-Salicide (CoSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )-Silicon Schottky diodes fabricated in scaled-down 0.18 mum CMOS technology. With low sheet resistance of optimized CoSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Si Schottky diode, the voltage multiplier using the diode resulted in superior power sensitivity compared to low-threshold (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) metal oxide semiconductor field effect transistors. Various multipliers with different diode sizes were fabricated and their sensitivities were compared. Under the operating current level of radio frequency identification (RFID) tag chips ( ~ muA), the voltage multipliers possessing smaller diodes showed better sensitivity due to higher <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor. An optimized five-stage voltage multiplier required an input power of - 19.5 dBm for a 1.2 V output voltage at 900 MHz. The measured sensitivity is the lowest for any UHF-band multiplier for passive RFID tag chips. This result based on scaled-down CMOS technology provides increased RFID operation range as well as higher processing power at lower power consumption.