Printed Polysilicon on Stretchable Substrate for Strain Sensor Applications

Abstract

Over the past few years, post-surgery monitoring has become an important aspect of the patient’s healthcare in the modern clinical medicine. This kind of monitoring is done to examine various physical and chemical parameters, while considering any post-surgery complications. Therefore, the patient’s care is continued even after the surgical treatment and any sudden complications can be prevented from this intensive monitoring. For this purpose, electronic implantable sensors are preferred to monitor the various required physiological factors such as blood pressure, body temperature, heart rate, etc. This kind of in-vivo measurements can be done by directly implanting the sensors at the afflicted site inside the patient’s body. Therefore, the implantable biosensors are commonly used to monitor and measure various parameters such as pressure, stress and strain, pH, and many others in a less invasive way.
As the implantable biosensors are directly placed on the tissue or organ for monitoring, the efficiency of sensing and mapping the required information can be achieved by maximal surface contact. This can be fulfilled with the help of the wide range of available flexible and stretchable materials such as polyimide, PDMS, and many more. Instead of the conventional IC fabrication process, printing technology is a better alternative to fabricate these flexible and stretchable biosensors at low cost with a great amount of substrate choices. Among the available semiconducting inks, liquid silicon proved to be a better choice in making devices with good performance. The term ‘liquid silicon’ refers to silicon-based polymers such as Polysilanes. Thus, the combination of liquid silicon based implantable biosensors on flexible and stretchable substrates has lot of potential to be explored.
In this thesis, the focus is to print a conductive polysilicon layer on a flexible and stretchable substrate. Initially, the substrate materials- Polyimide and PDMS are chosen as per the requirements of flexibility, stretchability, biocompatibility and mechanical stability. After the preparing the substrate, the liquid silicon is coated on top of the substrate and the wettability is adjusted during the coating with the help of UV light. This polysilane layer is crystallised using KrF excimer laser to form a polysilicon layer. Thus, the polysilicon layer of thickness of about 200 nm is formed on top of a flexible and stretchable substrate.
This work forms the basis for future work in which the polysilicon resistors can be fabricated to be used as piezoresistive strain sensors. It can be further explored to include other functionalities such as real-time monitoring and self-sufficient in terms of power, etc. The choice of materials can be further expanded to include bio-resorbable materials such as silk, gelatin, and many more.