Search

This work is about the design, manufacturing process and characterization of an interdigital capacitor (IDC) sensor for graphene based biosensing applications. Certain layouts with different active sensor area and linespace ratios are investigated with analytic models and simulation models. Furthermore chips are manufactured and characterized on wafer level among the electrical parameters resistance and capacitance. The sensors have been used, for the detection of biomarkers through a functional layer reduced graphene oxide, immobilized with biomolecules, and characterized with low frequency electrochemical impedance spectroscopy (EIS). The aim is to identify the sensor layout with the best sensitivity at low frequency.

Due to the growing numbers of elderly people in the world, who suffer from incontinence and are in the need of care, technologies are necessary to increase the effectiveness of nursing staff and enhance the hygiene for humans to improve life quality. For this reason a low cost humidity sensor system printed onto the substrate of a diaper with the novel organic conductive ink PEDOT:PSS (Poly (3,4-ethylenedioxythio-phene):Poly(styrene sulfonate)) was developed in previous work [1]. The novel material PEDOT:PSS is still expensive because of rare use in research and market demand. Therefore a way for optimization of the sensor is aimed to print the sensor with less material, but at the same time with no loss of sensitivity. With this purpose, two theoretical models are developed. An analytic model with geometrical based calculations and a Finite Element Analysis (FEA) simulation model, for deeper understanding of electric field effects with focus on the total capacitance of the sensor. To verify these theoretical models a characterization measurement of manufactured samples of previous work [1] is made, to obtain a comparison between every experimental method. For the theoretical models the necessary material parameters are characterized.

A novel capacitive sensor for measuring the water-level and monitoring the water quality has been developed in this work by using an enhanced screen printing technology. A commonly used environment-friendly conductive polymer poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) for conductive sensors has a limited conductivity due to its high sheet resistance. A physical treatment performed during the printing process has reduced the sheet resistance of printed PEDOT:PSS on polyethylenterephthalat (PET) substrate from 264.39 Ω/sq to 23.44 Ω/sq. The adhesion bonding force between printed PEDOT:PSS and the substrate PET is increased by using chemical treatment and tested using a newly designed adhesive peeling force test. Using the economical conductive ink PEDOT:PSS with this new physical treatment, our capacitive sensors are cost-efficient and have a sensitivity of up to 1.25 pF/mm.

The anodic bonding technology is a well-established industrial technique, which has been reported to account for the mainstream packaging methods in Micro-Electro-Mechanical-Systems (MEMS) devices, such as hermetic sealing, encapsulation, and wafer level packaging. It is widely recognized that the CTEs of many bondable materials are temperature dependent. The residual stress is induced between the bonding interface during the cooling process. This residual stress degrades the device's performance, e.g. its offset, linearity, sensitivity or dynamic behavior. Currently, the mainstream methods for improving anodic bonding performance focus on reducing the bonding temperature, using a thinner glass layer, or using materials with optimized CTE (similar to silicon over a wide temperature range) to reduce the residual stress. As we understand[1], decreasing the bonding temperature reduces the bond quality. In this work, the residual stress is investigated by using the classical lamination theory (CLT) and experiments. The experimental observation showed a good agreement with the CLT calculation method. The study illustrates an efficient methodology to estimate the residual stress in an anodically bonded pair which leads to some suggestions to optimize the design of wafer level packaging.