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High quality recording of neuronal activities and electrical stimulation require neurotechnical implants with appropriate electrode material. Iridium oxide (IrOx) is an excellent choice of material due to its biocompatibility, low electrochemical impedance, superior charge injection capacity, corrosion resistance, longevity, and electrochemical stability. Plasma enhanced atomic layer deposition (PE-ALD) and a suitable precursor, like (Methylcyclopentadienyl) (1,5- cyclooctadiene) iridium, could be a promising technique to produce highly conformal and performant IrOx-films at low temperatures and low costs. Various studies have reported the deposition of iridium oxide, but usually at very high temperatures. These processes are not suitable for polymer substrates and limit the use of such post-processing together with active implants. In this work the (Methylcyclopentadienyl) (1,5-cyclooctadiene) iridium(I) ((MeCp)Ir(COD)) precursor was used as a promising approach for depositing IrOx-films using low temperature PE-ALD. This precursor is normally used for chemical vapour deposition processes. First experiments were carried out on silicon substrates at deposition temperatures of 110 C°. The precursor was heated up to 75 °C and oxygen plasma was used as coreactant. The deposited films were analysed with EDX and AFM, showing a smooth surface and a promising ratio between the elements iridium and oxygen.

Encapsulation is essential for mechanically flexible and electrically active implants as it protects them from the harsh environment inside the body. Since the performance and longevity of implants depends on the quality of encapsulation, research continues into new and better encapsulation strategies. Chemical vapour deposition can be used to deposit Parylene-C, a biocompatible polymer, at room temperature. Plasma enhanced atomic layer deposition can be used to deposit ultra-thin, conformal, and hermetic metal oxide layers. These strategies are both used for the encapsulation of implants. In this work, these two methods are combined to create a polymer/metal oxide hybrid system in which a layer system of metal oxides is sandwiched between two Parylene- C layers. DC leakage-current measurement and elevated temperature are used to qualify the barrier property of the layer-system. After more than one year, the barrier properties still show no significant decrease.

No abstract

We consider an optimal control problem governed by an obstacle problem. The novelty and focus of this work will be the introduction of a control variable into the coefficients of this optimal control problem. In particular, we discuss the effects of the multiplicative coupling between control and, derivatives of, the state. This prevents the use of standard weak convergence arguments in limit arguments. As it is known, H‐convergence needs to be utilized, e.g., to prove existence of a solution to the problem. To obtain optimality conditions, we present a regularization approach to circumvent the non‐differentiability of the solution operator of the obstacle problems. We then discuss the limiting optimality conditions obtained by the proposed regularization.