An apparatus includes a sensor array with a plurality of active pixels. Each active pixel in the sensor array includes: a three transistor (3T) sensor with a source follower transistor, and a detection diode coupled in series to a parasitic capacitor at a sensing junction. A gate of the source follower transistor amplifier is coupled to the sensing junction. The apparatus includes an insulator layer over the sensor array. The insulator layer provides a variable capacitance to the sensing junctions of underlying active pixels in response to portions of an object being proximate to the insulator layer. The variable capacitance is used to detect an image of the object.