Highly Flexible Devices Based on Double Gated Organic Thin Film Transistor for Tactile Sensing

The realization of an artificial tactile sensing system is very challenging as requires the integration of different types of sensors into one system that should cover large and complex areas, while keeping fabrication costs low. In this respect, organic electronics represents a step forward as it allows for the development of flexible sensing systems capable to mimic the human skin mechanical properties and also its functionalities.
In this presentation, after revising some of the approaches reported recently in the literature, we will demonstrate that the employment of double gate organic transistor could be a valuable solution for the fabrication of flexible and highly sensitive multimodal tactile transducers.
In the first example we report the employment of a flexible sub-micrometer channel Organic Charge Modulated Field Effect Transistor (OCMFET) coupled with a pyro/piezoelectric element (i.e. a poly-vinylene difluoride (PVDF) film) for the fabrication of highly sensitive multimodal tactile transducers capable to simultaneous detect temperature and force. In particular, in such a case, the sensing devices are fabricated by using a vertical channel architecture, realized by means of up-scalable and low cost techniques. The reduction of the channel length, allowed to maximize the ratio between the sensing area and the transistor’s channel area, leading to considerably enhancement both in temperature and force sensitivity with respect to what previously reported.
In a second example we introduce a stacked double gated transistor structure. We will show, first of all, that using such architecture the performances of the fabricated devices, in terms of threshold voltage and carrier mobility, can be finely tuned by adjusting the two different gates potentials. We will demonstrate that also in this case it is possible to couple such devices with a pyro/piezoelectric element leading to obtain a self-powered force and temperature sensor with high sensitivity.
We will also demonstrate that both approaches can be employed for the fabrication of tattoo-like sensing systems. In particular, the developed systems have been fabricated on a plastic carrier, coated with a water-soluble material acting as sacrificial layer. At the top of such a structure, an ultrathin (sub-micrometer) film of parylene C is deposited. Finally, at the top of this structure the different kinds of electronic devices can be fabricated. Once the sensing systems fabrication is completed, the water-soluble layer can be dissolved allowing the transfer of the conformable sensing patch onto whatever kind of substrate, as skin, prosthetic hands or limbs, paper etc. This approach represents a valuable solution for the development of a wide range of applications moving from robotics, to smart wearable and smart packaging systems etc.