Alexander Türke

Flexible polymer humidity sensor fabricated by inkjet printing

In this paper a humidity sensor concept is presented which is fully fabricated by inkjet printing. In the first step conductive finger electrodes are inkjet printed on flexible polyimide substrate with a silver neodecanoate based ink. Afterwards a humidity sensitive layer is printed upon using a polymer particle based ink. Two approaches are presented for minimizing the line width of the electrode fingers. The humidity sensitivities of the sensor capacitances are investigated. The results are promising and demonstrate, that inkjet printed sensors are potentially suited for label applications. The achieved sensitivity, repeatability and hysteresis are in acceptable ranges.

Determination of the wine preservative sulphur dioxide with cyclic voltammetry using inkjet printed electrodes.

During winemaking sulphur dioxide is added to prevent undesirable reactions. However, concerns over the harmful effects of sulphites have led to legal limits being placed upon such additives. There is thus a need for simple and selective determinations of sulphur dioxide in wine, especially during winemaking. The simultaneous detection of polyphenols and sulphur dioxide, using cyclic voltammetry at inert electrodes is challenging due to close oxidation potentials. In the present study, inkjet printed electrodes were developed with a suitable voltammetric signal on which the polyphenol oxidation is suppressed and the oxidation peak height for sulphur dioxide corresponds linearly to the concentration. Different types of working electrodes were printed. Electrodes consisting of gold nanoparticles mixed with silver showed the highest sensitivity towards sulphur dioxide. Low cost production of the sensor elements and ultra fast determination of sulphur dioxide by cyclic voltammetry makes this technique very promising for the wine industry.

Inkjet printed humidity threshold monitoring sensor solution with irreversible resistance change for passive RFID applications

Continuous monitoring of environmental parameters to determine threshold or dosage violations is of strong interest throughout the life cycle of goods. The task is challenging, when there is no continuous supply of electric energy available and lowest cost sensor solutions are required - two common application constraints in passive RFID applications which are also required to fulfill monitoring tasks. Presented is a humidity threshold violation sensor concept, in which the exceedance of a humidity threshold value leads to a permanent sensor resistance change. The principle is based upon the deliquescence of salts as a threshold detection mechanism, as well as chemical sintering of metal nanoparticles, used as irreversible state change mechanism. The introduced sensor arrangement is completely inkjet printed. Several experiments demonstrate the feasibility of the approach. Due to the strong resistance change, the sensor elements can serve as humidity triggered switches in electric circuits as demonstrated by the integration into a freely programmable RFID UHF transponder tag.

Setup and properties of a fully inkjet printed humidity sensor on PET substrate

A fully ink jet printed humidity sensor on a thin PET foil is presented in this paper. Conductive silver electrodes were ink jet printed in the first step. Afterwards film forming polymer particles were printed on top as the humidity sensitive layer. Capacitance measurements were performed to investigate the sensor behavior at different humidity levels. By optimization of the electrode printing parameters the required sensor area was significantly reduced. Systematic investigations for the improvement of the humidity dependent layer led to a suitable polymer film, which combines good processability by inkjet printing with adequate humidity sensitivity and small hysteresis. The proposed sensor shows a high potential for low cost applications, which requires thin and flexible humidity sensors. For the correction of the nonlinear sensor transfer function a correction function with three calibration points is proposed.

Inkjet printed electrodes for determination of sulfur dioxide and ascorbic acid in wine

The determination of wine additives such as sulfur dioxide and ascorbic acid is motivated by limiting these substances because of their potential noxious effects. Cyclic voltammetry with inkjet printed electrodes on a PET foil was used to quantify free sulfur dioxide and ascorbic acid in a model wine solution. Two different kinds of electrodes were manufactured: Silver electrodes and silver electrodes modified with gold nanoparticles. Inkjet printed electrodes showed high sensitivity and selectivity towards ascorbic acid and sulfur dioxide and a linear relationship between concentration and peak current was observed. Modification of the inkjet printed silver electrode with gold nanoparticles increased the sensitivity. Additionally, more defined current peaks were obtained, that proved the excellent suitability of the silver electrodes modified with gold nanoparticles for precise determination of sulfur dioxide and ascorbic acid in wine.

Simultaneous detection of ascorbic acid and sulfur dioxide on a poly(3,4-ethylenedioxythiophene) covered gold electrode

For wine industry, the quality of the produced wine is very important. Sulfur dioxide (SO2) is used as an antioxidant and preservative. But also ascorbic acid plays an important role in preventing oxidation. Therefore, there is a need for detecting these components in wines. Cyclic voltammetry was used to determine SO2 and ascorbic acid in a pH 3.3 model wine solution. In literature, modified electrodes showed advantages compared to bare electrodes. For this reason a gold electrode covered with poly(3,4-ethylenedioxythiophene) (PEDOT) was used. In the simultaneous presence, well defined separated current peaks for SO2 and ascorbic acid were detected, which proved the excellent suitability of the PEDOT covered gold electrode for precise determination. A linear relationship between concentration and peak current was observed.

Ink-Jet Printing of Conductive Nanostructures

This chapter refers to the ink-jet printing process of different types of conducting inks. Ink-jet printing is a contactless, digital and additive deposition method. Although the throughput is not as high as other techniques (e.g. gravure or offset printing) ink-jet printing becomes more and more popular. Printing of conducting structures is one step of producing complex microsystems. Therefor the printing process and the annealing temperature of the conductive inks have to be optimized. Different approached are described in this chapter to realize a low cost ink-jet printing process on flexible substrate materials. Also a new type of ink is introduced to achieve low sintering temperatures.