13.56 MHz Organic Transistor Based Rectifier Circuits for RFID Tags
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13.56 MHz Organic Transistor Based Rectifier Circuits for RFID Tags Robert Rotzoll1, Siddharth Mohapatra1, Viorel Olariu1, Robert Wenz1,2, Michelle Grigas1, Oleg Shchekin2, Klaus Dimmler1 and Ananth Dodabalapur1,2 1
OrganicID, Inc., 422 East Vermijo Ave, Colorado Springs, CO
2
Microelectronics Research Center, The University of Austin, TX 78733
ABSTRACT One of the potential application areas for organic and polymers transistors is in radiofrequency identification (RFID) tags. One of the key components of an RFID tag is the front-end rectifier that must rectify a 13.56 MHz AC signal received from a resonant tuned antenna. The rectifier supplies operating power to the tag. Organic transistor circuits have hitherto not operated at this high frequency. We show that by operating pentacene transistors in the non-quasi-static (NQS) regime such operating speeds can be achieved in rectifier circuits. The circuits were fabricated on flexible plastic substrates and employed a solution-cast dielectric. The pentacene mobilities are in the range 0.1-1.5 cm2/V-s. The channel lengths of the transistors are in the range 2-4 µm. Full-wave NQS mode rectifiers were measured to have voltage rectification efficiency in excess of 28% at 14 MHz, demonstrating that such circuits can be used in RFID tags. These circuits operated successfully at speeds up to 20 MHz. INTRODUCTION Radio frequency identification (RFID) has been proposed as one of several areas for application of organic thin film transistors (OTFT) as performance and complexity of the devices has improved [1 - 6]. Operation of organic semiconductor field effect transistors is only viable to frequencies on the order of 1 MHz due to limitations on transistor mobility, gate length and methods of patterning [6]. It is clear that existing organic transistors support RFID operation at carrier frequencies of 125 kHz. OTFT operation at frequencies up to 20 MHz is now demonstrated for a power rectifier utilizing pentacene-based PMIS transistor integrated circuit on a polymer substrate. RECTIFIER ANALYSIS & DESIGN A typical RFID tag, Figure 1, contains three major functional blocks and an antenna coil. The antenna coil is used to magnetically couple radio frequency energy from an RFID reader into the tag. This energy is used to power the tag and provide bi-directional communications between the reader and the tag. A radio frequency (RF) energy rectifier in the RF Interface provides a DC power supply to the entire RFID tag and must operate at the
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Reg VDD Voltage Ref
Antenna Coil
RF Interface
Receive Data Power-On Reset
Digital Processor
Address
Clock
Read
Transmit Enable
Data
Data Memory
Transmit Data
Figure 1. RFID tag block diagram frequency of the signal from the antenna coil. This frequency is chosen as 13.56 MHz for use in item-level tag applications. NON-QUASI-STATIC RECTIFIER OPERATION In organic/polymer TFTs, non-quasi-static (NQS) operation of the transistors is established at frequencies above approximately 1 MHz. The transistor channel is mode
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