Transparent Pressure Sensor with High Linearity over a Wide Pressure Range for 3D Touch Screen Applications

The demand for display technology is expected to increase with the continuous spread of portable electronics and with the expected emergence of flexible, wearable, and transparent display devices. A touch screen is a critical component in display technology that enables user interface operations, and the future generation of touch screens, the so-called 3D touch screens, is expected to be able to detect multiple levels of pressure. To enable 3D touch screens, transparent pressure sensors with high linearity over a working range that encompasses the pressure range of human touch (10-100 kPa) are required. In this work, a transparent and linear capacitive pressure sensor is reported with a transmittance over 85% and high linearity (R² = 0.995) over 5-100 kPa of pressure. To render the sensor transparent, a microstructured "hard" elastomer layer was filled in with a refractive index matching a "soft" elastomer layer, through which light scattering was minimized. High linearity was attained from the sensor's unique architecture that increases the effective area of the capacitor with applied pressure. These attributes render our sensor highly suitable for future 3D touch screen applications.