Printed read-only memories and their operation in mobile readout system (Conference Presentation)

Printed read-only memory (ROM) would be a key component for many envisioned printed electronics applications such as item identification, anti-counterfeiting, brand protection and supply chain management. This paper will firstly introduce the electrical requirements on the memories to be operated in power constrained mobile readout systems for these targeted applications. Then, two types of printed ROMs, including polymer resistive type ROM and fuse-type electrically programmable write-once-read-many (WORM) ROM, will be presented. For the former, the instability issues associated with the conventional PEDOT: PSS and its interface with contact electrodes will be revealed. This work proves that, by removing the hydrophilic acidic groups in conventional PEDOT: PSS, these instability issues can be well addressed. The ROM tags fabricated based on the modified PEDOT: PSS of neutral pH and inkjet printed silver electrodes present extremely stable performance under both aging and electrical stress tests in air ambient. For the latter, fuse-type WORM ROMs are fabricated using a common material inkjet printer to form both the contact pads and the resistor tracks with the same silver ink and process settings. Based on the dependence of the fusing voltage on the length of the printed resistor track, a new cell structure is proposed to achieve multi-bit memories with greatly saved contact pad numbers for easier external electrical connections than the conventional design. The memory cells also present excellent long-term storage and operation stabilities. The function of the printed ROMs are finally demonstrated with mobile readout hardware systems.