Performance Comparison of Inkjet and Thermal Transfer Printed Passive UHF RFID Tags

We compare the maximum read range of passive ultra high frequency (UHF) radio frequency identification (RFID) tags that have been produced using different metal printing techniques, specifically inkjet printing and thermal transfer printing. We used the same substrate (THERMLfilm), antenna designs, and electronic circuitry in our comparison so as to isolate the effect of the metal printing. Due to the high metal conductivity, the thermal transfer printed tags printed with copper ink performed as well or better than the inkjet printed tags printed with silver ink, even when we changed the inkjet printed tags to a Kapton substrate that is better suited to inkjet printing. The aluminium thermal transfer printed tags had up to 33% less read range than copper thermal transfer printed tags. Thermal transfer printing needs no sintering, and provides an attractive alternative low-cost fabrication method. Characterisation of the printed traces by both methods reveals that the printing techniques achieve similar surface roughness between 19.8 nm and 21.2 nm RMS. The achieved conductivities for thermal transfer printing on THERMLfilm were 2.6⇥10 S/m and 3.9⇥10 S/m for aluminium and copper films respectively while inkjet printing achieved 1.7⇥10 S/m conductivity on the same substrate. The best measured read range