Objectives:

  • Μicromachined sensors with polymeric sensing layers for application in the monitoring of volatile organic compounds in the environment
  • Polymeric structures and devices for photonic applications

Sensing modules for real-time monitoring of harmful species in industrial sites

Gas sensing devices for monitoring the composition of the gaseous environment in real conditions, where humidity and temperature variations occurred, is of great interest, as the potential for their application across many industrial installations has become apparent. This is the consequence of engineering smaller sized sensing devices characterized by low cost fabrication and low power operation. Additionally, such sensing devices could form sensor networks for long term continuous and wireless sensing application.

The sensor or the sensors array should be appropriately designed for the targeted application and ideally should be either monolithically integrated with read–out electronics or hybrid integrated with commercially available ones. In this direction the use of chemocapacitor type sensors is promoted, with already proven promising results in terms of selectivity/sensitivity and reproducibility with potential application in measurements of complex gaseous environments. The configuration of planar InterDigitated Electrodes (IDEs) seems to be the most promising since it addresses the need of feasible fabrication and manageable disposal of the polymeric sensing material.

The selection of the optimum IDEs layout design is based on theoretical studies investigating the feasible fabrication with the gain in terms of sensitivity as electrodes critical dimension is miniaturized in conjunction with certain limitations arise by the hybrid integration of the miniaturized sensors with commercial available read out electronics. The optimum layout dimensions are identified by the relevant simulation data depicted in Figure 1. The very good agreement between experimental and simulation data verifies that the miniaturization of the IDEs critical dimension leads to systems with higher sensing performance. However, further miniaturization than 1.0μm W(=G) layouts contributes only to minor enhancement of the sensitivity while the resulting reduction of the sensing area in order to meet the read-out electronic specifications is restrictive due to fabrication constraints.

With appropriate micromachining/ microelectronic processing steps, as depicted in Figure 2, the fabrication of miniaturized IDE arrays with critical dimension of 1.0μm on Si wafer is realized, Figure 3. The use of EBL step provides a large scale functionality of the produced IDE layout. The adaptation of the particular fabrication procedure guarantees the realization of IDEs without electrical interference due to the use of thick dielectric layers as substrate and with reproducible polymeric layers properties.

A hybrid gas sensing module consisting of an 8-InterDigitated Chemocapacitive (IDC) sensor array and low power control and read-out electronics is developed. Each sensor of the sensor array is coated with different semi-selective polymeric layer. The evaluation of the sensing performance of the sensors involves exposure to Volatile Organic Compounds (VOCs) of interest in certain concentrations. The VOCs-targets stems from an on-going project on the development of a sensing system for the continuous monitoring of the workspace environment in printed flexing packaging industries. A typical example of dynamic measurement is illustrated in Figure 4. The normalized capacitance changes upon exposure to the analyte-target, for IDCs consisting of 2.0μm W(=G) and 1.0μm W(=G) IDE layouts covered with a relative hydrophobic polymeric material, are monitored. For all the examined vapour concentrations, an increase in sensitivity is achieved when the IDE layout is minimized. The experimental data are in agreement with the estimation of the simulation calculations.

 POLYMER_BASED_SENSOR_AND_SYSTEMS_img1  POLYMER_BASED_SENSOR_AND_SYSTEMS_img2

Figure 1: Comparison between experimental and simulation data of the sensing performance for IDCs with different IDEs configuration.

Figure 2: Fabrication flowchart of a sensor array. The fabrication consists of mainstream microelectronic/ micromachining processing steps.

 POLYMER_BASED_SENSOR_AND_SYSTEMS_img3POLYMER_BASED_SENSOR_AND_SYSTEMS_img4  POLYMER_BASED_SENSOR_AND_SYSTEMS_img5

Figure 3: SEM images of an IDE structure with measured critical dimension 1μm and SU-8 thick well around each sensing area of the 8-IDC sensor array

Figure 4: Dynamic normalized response of a PBMA coated sensor upon exposure to ethyl acetate vapours for IDE 1.0μm W(=G) and 2.0μm W(=G) layout respectively.

Design and realization of polymeric photonic filter arrays

1-D photonic crystals (PCs) are devices composed of sequential layers of materials with a refractive index contrast and therefore tunable reflectance properties. All approaches that have been proposed and applied so far proved to be reliable and can deliver 1-D PCs of very high quality and with tuned bandgap properties. However none of these technologies at their present form is able to realize 1-D photonic crystal arrays on the same substrate with different tuned optical properties.

 POLYMER_BASED_SENSOR_AND_SYSTEMS_img6

Figure 5: Schematic presentation of the fabrication of a Cross-PHEMA/Cross-EPR array having 4 different PCs. EPR and PHEMA act as lithographic materials.

In order to overcome this limitation, a methodology for the realization of 1-D polymeric PC arrays is introduced and optimized, fig. 5. Carefully selected patternable materials are applied via spin coating and each layer is processed via mainstream lithographic steps [Post Apply bake, Exposure, Post Exposure Bake and development]. Through this sequence of lithographic processing steps, 1-D polymeric PC structures are realized. The shape and the dimensions of each PC is defined through the lithographic mask and the lateral dimensions can be as small as few tens of micrometer. The photoresist formulations and the processing conditions applied in this technology have been carefully optimized in order to allow for the definition, during a single lithographic step, of patterns exhibiting the desirable variation in thickness (grey scale lithography). Due to the particular photopatternable materials used, the tuning of the thickness is possible for the two polymers independently, allowing for the realization of 1-D PC arrays e.g. as filters on top of already fabricated electronic devices, figs. 6-7.

 POLYMER_BASED_SENSOR_AND_SYSTEMS_img7POLYMER_BASED_SENSOR_AND_SYSTEMS_img8  POLYMER_BASED_SENSOR_AND_SYSTEMS_img9

Figure 6: SEM cross section of the 1-D PC and optical image of the final 1-D photonic crystal array

Figure 7: The reflectance spectra of each area of the PC array that is fabricated with the procedure described in fig. 5.

Group Members

Recent Publications in Peer Reviewed Journals

 

  1. 1-D Polymeric Photonic Crystals as Spectroscopic Zero-Power Humidity Sensors, M.-I. Georgaki, A. Botsialas, P. Argitis, N. Papanikolaou, P. Oikonomou, I. Raptis, J. Rysz, A. Budkowski, M. Chatzichristidi, Microelectronic Engineering (2014) 115, 55-58
  1. Chemocapacitive sensor arrays on Si substrate: towards the hybrid integration with read-out electronics, P. Oikonomou, A. Botsialas, A. Olziersky, D. Goustouridis, A. Speliotis, I. Raptis, M. Sanopoulou, Microelectronic Engineering (2014) 119, 11-16
  1. Immobilization of oligonucleotide probes on silicon surfaces using biotin-streptavidin system examined with microscopic and spectroscopic techniques, K. Awsiuk, J. Rysz, P. Petrou, A. Budkowski, A. Bernasik, S. Kakabakos, M. M. Marzec, I. Raptis, Applied Surface Science (2014) 290 199-206
  1. Monitoring and Evaluation of Alcoholic Fermentation Processes Using a Chemocapacitor Sensor Array, P. Oikonomou, I. Raptis, M. Sanopoulou, Sensors (2014) 14 16258-16270
  1. A miniaturized chemocapacitor system for the detection of volatile organic compounds, Botsialas A., Oikonomou P., Goustouridis D., Ganetsos Th., Raptis I., Sanopoulou M., Sensors and Actuators B, 177, pp. 776-784, 2013