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 (TFT) on the first surface of the substrate ; an electroluminescence element on the transistor (TFT); and an encapsulation unit 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 (TFT), a portion of the electroluminescence element , and a portion of the encapsulation unit 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 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 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 (TFT) on the first surface of the substrate ; an electroluminescence element on the transistor (TFT); and an encapsulation unit 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 (TFT), a portion of the electroluminescence element , and a portion of the encapsulation unit 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 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 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 (TFT) on the first surface of the substrate ; an electroluminescence element on the transistor (TFT); and an encapsulation unit 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 (TFT), a portion of the electroluminescence element , and a portion of the encapsulation unit 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 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 comprises a photo-chromatic material that can be turned from transparent to black when exposed to light of a particular wavelength. <EOS>