Dye based solar cells have been studied thoroughly in recent years. However, using this technology for dye based light sensors in polymer based systems offers several advantages compared to classical devices. A printable light sensor could be easily integrated into current smart label fabrication processes. Moreover, printable light sensors combined with novel conductive polymers could solve reliability issues resulting from bonding processes. In this paper we report on the fabrication of dye based light sensors using Ruthenium 535-bis-TBA as active dye and Iodide solution as charge transporting layer. A prototype has been developed and tested successfully. In order to improve the technology towards smart label integration, silica gel has been used to harden the Iodide liquid electrolyte. Depending on the silica gel concentrations, different stiffness levels can be achieved. Whereas the first light sensor prototypes have been made on glass substrates, the new ones are based on polymer substrates. The polymer foil KAPTON by Du Pont has been used as substrate. Special care has to be taken regarding the preparation of the transparent electrodes. The transparent conductive oxide (TCO) Indium Tin Oxide (ITO), which has been used as transparent electrode, has to be cured at elevated temperatures.
In conclusion we have shown that dye based light sensors can be used for the integration into smart labels. Moreover modifications in the process lead to a light sensor which is compatible to future polymer based systems.
The aim of this paper is to present an integrated process flow for a smart tag with integrated sensors and RFID
communication, a Flexible Tag Microlab (FTM). The heart of the designed container tracing system is an RFID system
(Reader + Tag) with gas sensing capabilities on board. In the former prototypes, the chemical sensors were integrated on
the reader, whereas the tags where addressed like conventional RFID-tags containing also physical (temperature,
humidity and light) sensors. However, this paper will show how the gas sensing reader functionalities are being
transferred to the tag, reaching a flexible tag microlab, which represents a real innovation in the field of flexible labels.
Key issues for the realisation of the FTM, such us flexible substrates and gas sensor integration technologies will be
The process flow employed for the two metal levels interconnect fabrication will be described in detail. The material
used is the DuPont<sup>TM</sup> Pyralux<sup>(R)</sup> AP 8525R double-sided copper-clad laminate, formed by a Kapton foil with a copper
layer on each side. The vias and windows openings are performed by femtosecond laser ablation. The copper
interconnections are realized by photolithography and wet chemical etching.
The MOX sensors hotplates specially developed to fulfil the FTM constrains in terms of low power consumption has
been used to prove two integration technologies into the flexible substrates: Chip on Flex (COF) wire bonding and
Anisotropic Conductive Adhesive (ACA) flip chip bonding. Both technologies will be compared and benchmarked for
future product developments.
A multisensing flexible Tag microlab (FTM) with RFID communication capabilities and integrated physical and
chemical sensors for logistic datalogging applications is being developed. For this very specific scenario, several
constraints must be considered: power consumption must be limited for long-term operation, reliable ISO compliant
RFID communication must be implemented, and special encapsulation issues must be faced for reliable sensor
integration. In this work, the developments on application specific electronic interfaces and on ultra-low-power MOX
gas sensors in the framework of the GoodFood FP6 Integrated Project will be reported.
The electronics for sensor control and readout as well as for RFID communication are based on an ultra-low-power
MSP430 microcontroller from Texas Instruments together with a custom RFID front-end based on analog circuitry and
a CPLD digital device, and are designed to guarantee a passive ISO15693 compliant RFID communication in a range up
to 6 cm. A thin film battery for sensor operation is included, allowing data acquisition and storage when no reader field
is present. This design allows the user to access both the traceability and sensor information even when the on-board
battery is exhausted.
The physical sensors for light, temperature and humidity are commercially available devices, while for chemical gas
sensing innovative MOX sensors are developed, based on ultra-low-power micromachined hotplate arrays specifically
designed for flexible Tag integration purposes. A single MOX sensor requires only 8.9 mW for continuous operation,
while temperature modulation and discontinuous sensor operation modes are implemented to further reduce the overall
The development of the custom control and RFID electronics, together with innovative ultra-low-power MOX sensor
arrays with flexible circuit encapsulation techniques will be reported in this work.