An apparatus, comprising: a display device comprising: a substrate including a first surface and a second surface that is under the first surface; a transistor on the first surface of the substrate; an electroluminescence element on the transistor; and an encapsulation unit (128, 130, 132) on the electroluminescence element; said apparatus further comprising an ultrasonic fingerprint sensor that has been adhered under the second surface of the substrate; wherein a portion of the substrate, a portion of the transistor, a portion of the electroluminescence element, and a portion of the encapsulation unit (128, 130, 132) that overlap the ultrasonic fingerprint sensor are an ultrasonic transmission and reception channel on the ultrasonic fingerprint sensor; characterized in that a support substrate is arranged between the substrate and the ultrasonic fingerprint sensor, wherein said support substrate (160, 162, 174) comprises a thermo-chromatic material that can vary in visible light absorption rate when heated above a predetermined threshold temperature, thereby changing the color from transparent to opaque, or said support substrate (160, 162, 174) comprises a photo-chromatic material that can be turned from transparent to black when exposed to light of a particular wavelength. a display device comprising: a substrate including a first surface and a second surface that is under the first surface; a transistor on the first surface of the substrate; an electroluminescence element on the transistor; and an encapsulation unit (128, 130, 132) on the electroluminescence element; said apparatus further comprising an ultrasonic fingerprint sensor that has been adhered under the second surface of the substrate; wherein a portion of the substrate, a portion of the transistor, a portion of the electroluminescence element, and a portion of the encapsulation unit (128, 130, 132) that overlap the ultrasonic fingerprint sensor are an ultrasonic transmission and reception channel on the ultrasonic fingerprint sensor; characterized in that a support substrate is arranged between the substrate and the ultrasonic fingerprint sensor, wherein said support substrate (160, 162, 174) comprises a thermo-chromatic material that can vary in visible light absorption rate when heated above a predetermined threshold temperature, thereby changing the color from transparent to opaque, or said support substrate (160, 162, 174) comprises a photo-chromatic material that can be turned from transparent to black when exposed to light of a particular wavelength. a substrate including a first surface and a second surface that is under the first surface; a transistor on the first surface of the substrate; an electroluminescence element on the transistor; and an encapsulation unit (128, 130, 132) on the electroluminescence element; said apparatus further comprising an ultrasonic fingerprint sensor that has been adhered under the second surface of the substrate; wherein a portion of the substrate, a portion of the transistor, a portion of the electroluminescence element, and a portion of the encapsulation unit (128, 130, 132) that overlap the ultrasonic fingerprint sensor are an ultrasonic transmission and reception channel on the ultrasonic fingerprint sensor; characterized in that a support substrate is arranged between the substrate and the ultrasonic fingerprint sensor, wherein said support substrate (160, 162, 174) comprises a thermo-chromatic material that can vary in visible light absorption rate when heated above a predetermined threshold temperature, thereby changing the color from transparent to opaque, or said support substrate (160, 162, 174) comprises a photo-chromatic material that can be turned from transparent to black when exposed to light of a particular wavelength.