Encapsulation, bio-functionalization or electronic-cell interface – Atomic Layer Deposition enables new applications in medical technology

At Fraunhofer IMS it is possible to completely encapsulate active implants, since the ALD processes are adapted to the conformal coating of 3D objects. The materials are chosen in such a way that they are biocompatible and stable in the respective body environment.

It has been shown that the lifetime of active implants in a moist body environment can be increased enormously by additional ALD encapsulation. The advantage over a rigid titanium housing is the small space requirement, which plays a decisive role in the field of extreme miniaturization.

An "intelligent encapsulation" can be achieved by adding a sensory ALD layer. In this way, an encapsulation was developed at Fraunhofer IMS, which independently and equally monitors the entire surface of the implant for damage. This is achieved by continuously monitoring moisture levels within the implant. Another sensory property of ALD layers in this context is pH sensitivity.

The functionalization and precise adjustment of surfaces offers many advantages in the bio-medical field. In a fluidic cell system, the hydrophilicity of the chip surface has been adjusted in such a way that the liquid – and thus the cells it contains – can be optimally transported. Antibacterial or sterilizable properties, which play a major role in the medical environment, can also be applied to the surface using the ALD processes.

Intracellular measurements can be carried out with conductive and ultra-thin nanoneedles made of ALD materials, with diameters in the nanometer range. The needles are designed in such a way that they can penetrate into the interior of the cell and read out the electrical impulses there. The nanoneedles as array were attached directly to one CMOS circuits to be suitable for the parallel read out of several cells. Since the electronic circuit would be damaged by temperatures of over 400 °C, the specified temperature budget was considered during process development. Initial measurements have shown that the cells accept penetration of the nanoneedles and that they still emit electrical signals that can be derived accordingly.

A future field in the area of ALD are 2D materials, which is being promoted in the new Attract group "Ultra-thin transition-metal dichalcogenides for surface-modified functional layers" headed by Prof. Anjana Devi.

Due to the extremely large surface relative to nearly no volume, many sensory and functional properties are more present. First investigations were carried out in this area at Fraunhofer IMS with MoS₂. It was shown that MoS₂ can be deposited using ALD and first characterizations of the material properties were promising.