Monique J. Beenhakkers

Unipolar Organic Transistor Circuits Made Robust by Dual-Gate Technology

Dual-gate organic transistor technology is used to increase the robustness of digital circuits as illustrated by higher inverter gains and noise margins. The additional gate in the technology functions as a VT-control gate. Both zero-VGS-load and diode-load logic are investigated. The noise margin of zero- VGS-load inverter increases from 1.15 V (single gate) to 2.8 V (dual gate) at 20 V supply voltage. Diode-load logic inverters show an improvement in noise margin from ~0 V to 0.7 V for single gate and dual gate inverters, respectively. These values can be increased significantly by optimizing the inverter topologies. As a result of this optimization, noise margins larger than 6 V for zero- VGS-load logic and 1.4 V for diode-load logic are obtained. Functional 99-stage ring oscillators with 2.27 μs stage delays and 64 bit organic RFID transponder chips, operating at a data rate of 4.3 kb/s, have been manufactured.

A 128b organic RFID transponder chip, including Manchester encoding and ALOHA anti-collision protocol, operating with a data rate of 1529b/s

Research towards 13.56MHz organic RFID tags is one of the drivers for the field of organic electronics. A capacitively-coupled 64b organic RFID tag operating at 125kHz was demonstrated in [1]. Inductively-coupled 64b organic RFID tag operating at 13.56MHz were reported in [2,3].

An Inductively-Coupled 64b Organic RFID Tag Operating at 13.56MHz with a Data Rate of 787b/s

RFID systems operating at a base carrier frequency of 13.56 MHz can use low-cost inductive antennas on foil. In parallel to this coil, a capacitor on foil is used for matching the resonance frequency at 13.56 MHz. This LC-antenna detects the signal transmitted by the reader and energizes the organic rectifier with an AC-voltage at 13.56 MHz. From this voltage the rectifier generates the DC supply voltage for the 64 b organic transponder chip, which drives the modulation transistor between the on and off state with a 64b code sequence.

Robust digital design in organic electronics by dual-gate technology

Research towards organic RFID tags is one of the drivers of organic electronics. In recent years, 64b organic RFID tags have been shown with capacitive coupling [1] and inductive coupling at 13.56 MHz [2,3]. Recent improvements were a 128b organic transponder chip with basic anti-collision and Manchester encoding [4] and a first 4b tag in complementary organic technology [5].

Organic RFID Tags

Organic RFID tags are increasingly gaining credibility as a possible low-cost barcode replacement for product identification. This will only happen if organic RFID tags can operate in the frequency range defined by well-accepted EPC standards. This chapter evaluates the performance of existing organic RFID demonstrators and confirms that, based on lab scale demonstration of organic RFID tags, performance comparable to the EPC standards can be obtained. Moreover, the integration of sensors with the tags will enable added functionality and applications beyond pure identification.

Towards EPC-Compatible Organic RFID Tags

In this chapter, fully integrated organic RFID tags are demonstrated. These tags are inductively-coupled at a base frequency of 13.56 MHz and can be read out at distances up to 10 cm, which is the expected readout distance for proximity readers. We also demonstrate next generation transponder chips, fabricated in a dual-gate technology. The additional gate, backgate, is used to control the threshold voltage and allows integration into more robust unipolar, dual-VT transponder chips. Finally, we realized an 8-bit transponder chip having data rates that are EPC-compatible. This has been achieved in our thin-film transistor technology by introducing a high-k Al2O3 gate dielectric, by scaling the channel lengths down to 2 mm and by reducing the overlap capacitance of the parasitic source-gate and drain-gate capacitors.