Dennis Weber

Bidirectional Communication in an HF Hybrid Organic/Solution-Processed Metal-Oxide RFID Tag

A bidirectional communication protocol allows radio-frequency identification (RFID) tags to have readout of multiple tags in the RF field without collision of data. In this paper, we realized bidirectional communication between a reader system and thin-film RFID tag by introducing a novel protocol for the uplink communication. Amplitude modulation on the 13.56-MHz base carrier is used to transmit the uplink clock, whereas the data is modulated by varying pulsewidths on this clock. The technology for the thin-film RFID tags combines metal-oxide n-type transistors with organic p-type transistors resulting in a hybrid complementary technology flow. The design of the RFID tag comprises of two metal-oxide transistor rectifiers and a comparator to decode the data transmitted by the reader and different code generators that send 8 bits or 96 bits to the reader.

Functionalized ZnO nanoparticles for thin-film transistors: support of ligand removal by non-thermal methods

A new approach is presented which allows substantial reduction of the process temperature of zinc oxide nanoparticles to generate semiconducting thin films. Functionalization is used to allow facile dispersion and to prevent agglomeration of the particles. Since charge transport is impeded by an insulating shell of octylamine the functionalization needs to be removed. Particles are deposited by spin-coating and the resulting film is exposed to different treatments. It is shown that plain annealing processes require high temperatures to fully remove the capping agents. The method presented in this work is a combination of UV irradiation of the wet films before annealing to cleave the octylamine and a vacuum process to aid the removal of organic residues. The effectiveness of the method is proven by electrical characterization.

Base-etch removal of a ligand shell in thin films of ZnO nanoparticles for electronic applications

Functionalized nanoparticles offer many advantages regarding homogenous film formation. However, to utilize the semiconductive properties of metal oxides the insulating species on the particles surface need to be removed. A widely employed route is the thermal decomposition of the ligands. If one wishes to lower the process temperature it is necessary to find alternative procedures. The organic nature of the ligand shell of octylamine-functionalized ZnO nanoparticles is a contrast to the properties of the inorganic metal oxide. This discrepancy is used to aid the ligand removal by potassium hydroxide etching. Wet etching processes are widespread in the semiconductor industry. We report on the beneficial effect of a mild base treatment on the electrical properties of ZnO-based thin-film transistors. The annealing temperatures can be drastically reduced; a field effect mobility value of 0.1 cm2 V−1 s−1 was obtained at a maximum process temperature of 350 °C.

Soluble Metal Oxo Alkoxide Inks with Advanced Rheological Properties for Inkjet-Printed Thin-Film Transistors

Semiconductor inks containing an indium-based oxo alkoxide precursor material were optimized regarding rheology requirements for a commercial 10 pL inkjet printhead. The rheological stability is evaluated by measuring the dynamic viscosity of the formulations for 12 h with a constant shear rate stress under ambient conditions. It is believed that the observed superior stability of the inks is the result of effectively suppressing the hydrolysis and condensation reaction between the metal oxo alkoxide precursor complex and atmospheric water. This can be attributed to a strong precursor coordination and the resulting reduction in ligand exchange dynamics of the solvent tetrahydrofurfuryl alcohol which is used as the main solvent in the formulations. It is also shown that with a proper selection of cosolvents, having high polar Hansen solubility parameter values, the inks drop formation properties and wettability can be fine-tuned by maintaining the inks rheological stability. Good drop jetting performance without satellite formation and high drop velocities of 8.25 m/s were found with the support of dimensionless numbers and printability windows. By printing single 10 pL ink dots onto short channel indium-tin-oxide electrodes, In2O3 calcination at 350 °C and a solution-processed back-channel protection, high average saturation mobility of approximately 10 cm2/(V s) are demonstrated in a bottom-contact coplanar thin-film transistor device structure.