Touch is a dominant sense that allows us to experience the word around us. Most of today's electronic devices incorporate a capacitive touch interface, which is the prevalent technology in mobile phones and tablets to electronic appliances. However, capacitive touch fails to provide the rich experience associated with human touch – more specifically, the notion of touch “depth” or force. They are also harder (more costly) to adopt on a new generation of foldable electronic devices under development by electronic device manufacturers such Samsung, Huawei, Motorola and others. This emerging, foldable, form factor offers users the benefit of a multi-function device with a large area display that can also fold to fit comfortably in one’s pocket or bag. In these cases, the shift to thinner and flexible materials increases the noise levels associated with capacitive touch, thus increasing false-touch occurrences and typically requiring costly compensating solutions.

Peratech Holdco Ltd develop force-sensing solutions using a resistive-based technology, which allows both location and force input to be detected. In this project, the Fellow will explore the integration of Peratech’s sensing technology within the stack-up of a display module. Adding the touch interface directly into the display instead of above or below it can help to minimise display thickness (vital for foldable displays) and reduces the number of individual processes and layers that need to be assembled together in the final device.

To achieve this, I will lead the development of a miniaturised form of Peratech’s force sensing QTC™ ink technology, and an ink deposition process which allows it to be integrated within a display structure. This is no simple task, as the individual sensing elements must fit within the ‘black matrix’ of the display technology between the pixel assemblies, requiring patterning down to at least 30um size. New materials are needed which are optimised for a digital deposition process, including miniaturisation of the functional particles and optimising the rheology of the ink system to match the deposition process. To achieve this, I will collaborate with Printed Electronics Ltd, who are experts in digital, inkjet and other printing methods for manufacturing electronics systems.

The new ink system will be used to develop force-sensing arrays (with individual elements down to 30um in size) which provide a tunable resistance proportional to the force input. The array design will be optimized to give the required properties, and this will be aided by the concurrent development of computational simulations which can predict array performance based on the design features. Electronic systems to drive the sensel array will be produced, along with signal processing algorithms to convert sensel resistance into a signal from which touch location and touch force can be extracted. This will be used to demonstrate the functionality of the sensel array as a ‘3D’ touch interface which can provide a wealth of new experiences to the user.

Integration into a display module is the ultimate goal of the project. This involves interspersing the sensing elements between the pixel arrays present within a display technology (for example OLED or OLCD), i.e. building the sensel structures directly onto the ‘black matrix’ between pixels. To aid with this, display panels will be provided by FlexEnable Ltd, a leading organic-based display developer.

Successful development of this technology offers significant potential to both Peratech and the wider touch interface industry. It offers a step-change in how users can interact with their displays (for example mobile phone screens), turning a flat 2D surface into a rich, tactile experience which offers a more intuitive and adaptable touch interface.