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IGZO Thin Film Transistor Biosensors Functionalized with ZnO Nanorods and Antibodies

Professor Jian-Jang Huang's laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We demonstrate a biosensor structure consisting of an IGZO (Indium-Gallium-Zinc-Oxide) TFT (thin film transistor) and an extended sensing pad. The TFT acts as the sensing and readout device, while the sensing pad ensures the isolation of biological solution from the transistor channel layer, and meanwhile increases the sensing area. The biosensor is functionalized by first applying ZnO nanorods to increase the surface area for attracting electrical charges of EGFR (epidermal growth factor receptor) antibodies. The device is able to selectively detect 36.2 fM of EGFR in the total protein solution of 0.1 ng/ml extracted from squamous cell carcinoma (SCC). Furthermore, the conjugation duration of the functionalized device with EGFR can be limited to 3 minutes, implying that the biosensor has the advantage for real-time detection.

Figure 1 Experimental flow of the biosensing. The protein solution of EGFR antibody was first extracted from SCCs. Bio-Rad protein assay was used to determine total protein concentration. The 100g/ml SCC protein solution was decimally diluted to 10 g/ml, 1g/ml, 100 ng/ml … 0.1 ng/ml. The electrical responses after applying the total protein solution were then extracted from the functionalized TFT sensor.

Figure 2 Electrical properties of the biosensor. The corresponding drain currents and current increments at various total protein concentrations are demonstrated.

All-optical switching in GaAs microdisk resonators by a femtosecond pump-probe technique through tapered-fiber coupling

Professor Ming-Hua Mao's laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We demonstrate ultrafast all-optical switching in GaAs microdisk resonators using a femtosecond pump–probe technique through tapered-fiber coupling. The temporal tuning of the resonant modes resulted from the refractive index change due to photoexcited carrier density variation inside the GaAs microdisk resonator. Transmission through the GaAs microdisk resonator can be modulated by more than 10 dB with a switching time window of 8 ps in the switch-off operation using pumping pulses with energies as low as 17.5 pJ. The carrier lifetime was fitted to be 42 ps, much shorter than that of the bulk GaAs, typically of the order of nanoseconds. The above observation indicates that the surface recombination plays an important role in increasing the switching speed. This work has been published in Optics Letters, Vol. 39, No. 17, pp. 4998, (2014).

Fig. 1. Scanning electron microscope image of the fully processed microdisk cavity with a diameter of 10 μm.

Fig. 2. Switch-off dynamics with modulation depth more than 10 dB.

Very Closely Located Dual-band Frequency Selective Surfaces via Identical Resonant Elements

Professor Yih-Peng Chiou's laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Very closely located dual-band frequency selective surfaces (FSSs) are proposed. The ratio of two operating bands can be as low as 1.06. The proposed FSSs comprise simply a single-layer metallic pattern on a thin dielectric substrate. The mechanism to achieve the low ratio between two operating bands is attributed to two separated resonant modes caused by four identical elements in a unit cell. Asymmetrical meandered pattern is introduced to improve stability of frequency responses with respect to incident angles. Moreover, the ratio of the operating bands can be tuned through rotation of the elements with ratios in the range from 1.06 to 1.10. In order to validate the designs, the prototype of the dual-band FSSs has been fabricated and tested. And the measured results show good agreements with the simulated ones. This work is submitted to IEEE Antennas and Wireless Propagation Letters and accepted for publication.

Fig. 1. (a) The prototype of proposed very closely located dual-band FSSs, comprising a single layer metallic elements of 0.357 mm linewidth on a 0.23 mm FR4 substrate (ϵ_r = 4.4, loss tangent=0.02) with periodicity of 20 mm. The size of the prototype is 840 mm× 580 mm. (b) The measured S₂₁ of the prototype along with the full-wave results which FSSs with 0.23 mm FR4 substrate of ϵ_r = 4.4 and ϵ_r = 4.6 (loss tangent=0.02) are simulated, respectively.

Simulating an optical target to eliminate impinging beam in a light scattering simulations

Professor Snow H. Tseng's laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

In a light scattering simulation, light impinging upon the target position needs to be appropriately eliminated or else the continuously impinging light becomes a source of noise as it further reverberates through the random media. We report an optical target that eliminates incident waves to drain out the incoming energy. We show that the proposed optical target can absorb impinging light upon it from arbitrary directions. The performance of the optical target is analyzed and discussed.

Fig. Displacement of the CPML absorber causes imperfect elimination of the incident wave. An isotropic converging circular wave with the CPML displaced by various distances is simulated: (a) 0 μm, (b) 1 μm, (c) 4 μm from the center. The elimination effectiveness depends on the displacement. The error as a function of displacement is shown in (d).

Wide-angle and ultra-thin camera module using a curved hexagonal microlens array and all spherical surfaces

Professor Guo-Dung J. Su's laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We propose a wide-angle and thin camera module integrating the principles of an insect’s compound eye and the human eye, mimicking them with a curved hexagonal microlens array and a hemispherical lens, respectively. Compared to typical mobile phone cameras with more than four lenses and a limited full field of view, the proposed system uses only two lenses to achieve a wide full field of view. Furthermore, the thickness of our proposed system is only 2.7 mm. It has an f-number of 2.07, an image diameter of 4.032 mm, and a diagonal full field of view of 136°. The results showed good image quality with a modulation transfer function above 0.3 at a Nyquist frequency of 166 cycles/mm. This work has been published in Applied Optics, Vol. 53, Issue 29, pp. H121-H128 (2014).

Fig.1 Oblique view of curved hexagonal MLA. Each lens diameter is 500 μm, and the substrate radius is 2 mm.

Fig.2 Image simulation and processing of whole CMOS sensor.