In this letter, a scan driver circuit that can generate scan signals only in a selected area is proposed. It refreshes only the area that needs to be updated without refreshing the whole display. The proposed circuit with ten stages was fabricated using oxide thin film transistors. The additional area for selective driving occupies only 14.5 % of the unit stage area. This study confirms that the power consumption in the data lines and pixels for a dot pattern can be reduced by 25 % and 37.5 % when 50 % and 25 % of scan lines are selected, respectively.

This paper proposes a new architecture for a micro light emitting diode (micro-LED) display featuring fingerprint detection without any additional light emitting and sensing devices in mobile applications. This paper proposes that conventional LEDs can be used as photodetectors in active-matrix pixel circuits. In the area where a finger touched, some LEDs are used as photodetectors and others are used as light emitting sources. The photocurrents of reverse-biased LEDs under various illumination conditions were investigated. The active-matrix circuit was fabricated using a conventional p-type low-temperature polycrystalline silicon (LTPS) process. The fabricated pixel circuit could distinguish the intensity of the incident light to the sensing LED. The voltage across the sensing LED (VLED) was investigated when the pixel density was 400 pixels per inch (ppi) and the cover glass thickness was 30 μm. The experimental results showed that the VLED changed by 0.5 V for 16.7 ms when red, green, or blue LEDs emitted 150 cd/m 2 , 400 cd/m 2 , or 100 cd/m 2 , respectively. 19 LED array with 1.5 mm pitch (p) and 2 mm thick cover glass was fabricated to emulate the LED display with 400 ppi and 30 μm thick cover glass. It is found that an emitting LED affected the sensing LEDs within the distance of 3p by comparing VLEDs. VLEDs were measured when the material on the cover glass was air and water with white pigments (water/W). ΔVLEDs were 0.29 V and 1.13 V for glass-air and glass-water/W cases, respectively. It is found that the lights incident on the sensing LED comprised not only reflected lights by Fresnel reflection at the glass interface but also scattered lights in the water/W. A 75 magnified fake fingerprint was fabricated. Its material was poly-lactic acid with refractive index of 1.465 which is very close to that of a fingertip. Measured ΔVLEDs at ridges and valleys were 0.48 V and 0.22 V, respectively. The ratio of 0.48 / 0.22 was 2.18 that is very close to 1.91 that is the ratio of light intensity at the ridge to that at the valley obtained by the calculation. This verifies that the proposed micro-LED display distinguishes the ridges and valleys of fingerprint without any help from any additional devices.

A mismatch between the interpupillary distance (IPD) and inter-optical system distance (IOSD) in virtual reality (VR) applications can lead to discomfort. The IOSD must be adjustable according to the user's IPD to solve this issue. In this study, we investigate IPD estimation methods by tracking eye movements such as conjugate eye movement (CEM) and vergence. We hypothesize that the distance between the two pupils maintained during the CEM and is identical to the IPD. The vergencebased method induces eye divergence and determines the IPD as the maximum distance between pupils. Experiments with visual stimuli to induce CEM and divergence were conducted. The average errors of the estimated IPDs for the CEM-based and vergence-based methods were 2.06 and 1.30 mm, respectively. Furthermore, the analysis results show that the proposed methods can effectively reduce the IPD-IOSD difference and are especially helpful for users with a small IPD. If the IOSD is adjusted to the IPD estimated by the proposed methods, then VR discomfort can be eliminated.INDEX TERMS Eye movement, head-mounted display (HMD), interpupillary distance (IPD), IPD measurement, virtual reality (VR) device.

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This paper proposes a novel active-matrix (AM) micro light-emitting diode (micro-LED) display architecture featuring fingerprint detection. A new pixel circuit comprising four transistors and one capacitor (4T1C) is proposed to compensate for threshold voltages externally. The proposed AM micro-LED display does not need any additional light sources and sensors because an LED itself can be used for photosensors. The proposed 4T1C pixel circuit can isolate the effects of LED photocurrents caused by ambient lights and large LED capacitance from detecting the threshold voltage via external circuits. The proposed AM pixel circuit with oxide thin film transistors was fabricated using oxide thin film transistor process. The charges caused by the LED photocurrents were accumulated for 16.7 ms. The final voltages measured after 16.7 ms were -5.02 V and -1.53 V under irradiance of 0.05 W/m 2 and 1.54 W/m 2 , respectively. It is verified that the proposed micro-LED pixel circuit could distinguish incident lights reflected from ridges and valleys of a fingerprint.