This paper presents a newly developed square law detector array whose NEP is as low as ~ 1 pW/Hz<sup>0:5</sup> for 1.0 THz waves. The detector array using high electron mobility transistor (HEMT) with InGaAs/InAs/InGaAs double hetero-structured channel has been fabricated. The InAs-HEMT was fabricated on a quartz substrate using the layer transfer technology. Also, an array of square law detectors was developed by applying advanced selective etching, atomic layer deposition, and metallization to the transferred hetero-structured layers. The static analysis revealed that the transistor shows electron mobility as high as 3,200 cm<sup>2</sup>/Vs and low leakage with subthreshold slope as low as ~ 100 mV/dec. Detection performance was characterized by directly inputting 1.0 THz waves thorough a THz probe to each of the arrayed detectors. It is also demonstrated that the detection characteristics were well described by the analytical formulae derived from the channel-carrier behavior model. The experimental results suggested that the developed detector array is a promising candidate for imaging application.
The application using the frequency range from 100 GHz to 10 THz has attracted much attention, especially in broadband and higher data-rate wireless communication. In the THz broadband wireless devices, photo mixing by using the uni-traveling carrier photodiode (UTCPD) on the indium phosphide (InP) substrate is a crucial component. UTCPD can down-convert the optical signal to THz wave. To reduce the loss of the connection area between the optical section and the THz section, THz-band antennas and transition lines should be fabricated on the same substrate as the optical section. In our previous research, 1 x 4 and 4 x 4 planar array antennas using one-sided directional slot dipole antenna elements and branched coplanar waveguide (CPW) are connected to the output of UTCPD on the InP substrate for the 300 GHz application. In this presentation, wideband 600 GHz one-sided directional slot antenna was designed. The antenna is based on the slot antenna on the top with the bottom floating metal layer. To enhance the bandwidth, round shape of the edge of the top metal layer was introduced. Moreover, 2 kinds of the antenna element with different resonance frequencies are designed. Antenna 1 (Ant1) has a center frequency = 600 GHz and gain = 2.23dBi. Antenna 2 (Ant2) has a center frequency = 650 GHz and gain = 3.28dBi. The whole size of the antenna elements is 290 um x 230 um and 280 um x 290 um, respectively. Each antenna element is connected to the UTCPD and optical waveguide through a coplanar waveguide (CPW) feed line. Next, we designed a 2-dimensional antenna array with 12 antenna elements. To enhance the bandwidth 4 Ant1s and 8 Ant2s are combined on the InP substrate. From the electromagnetic simulation, this array antenna has antenna gain = 11.89 dBi, 3-dB bandwidth =130 GHz and front-to-back ratio = 15.73 dB. The array size is 1,500 um x 1,500 um. The relative bandwidth can be enhanced from 5 % (reference array antenna) to 20 %. Moreover, by changing the delay line attached to the optical fiber, it is easy to obtain the phase difference of each antenna element. From the results, our proposed phased array antenna has a wideband, high gain and beam tilt characteristics.
The terahertz (THz) wave applications at frequencies from 100 GHz to 10 THz has attracted much attention, especially in a broadband wireless communication. In the THz broadband wireless devices, photo mixing by using the unitraveling- carrier photodiode (UTC-PD) on the InP substrate is a critical issue, which is down-converted to the optical signal to THz wave. In this situation, the loss in the THz section is a serious problem. Therefore, antennas and transition lines should be fabricated on the same substrate. In our previous research, 1 x 4 and 4 x 4 planar array antennas using one-sided directional slot dipole antenna elements and branched coplanar waveguide (CPW) connected to the output of UTC-PD on the InP substrate is designed. In this paper, 4 x 4 phased array antenna on InP substrate for 300 GHz broadband telecommunication is demonstrated. The total antenna size is 1,930 μm x 2,000 μm x 18 μm. Four 1 x 4 subarray antenna are stacked planarly, and each subarray antenna is connected to the UTC-PD through the CPW. Each antenna element is arranged at the distance of half wavelength in order to sharpen the directivity. By changing the delay line attached to the optical fiber, the phase difference of each subarray can be obtained. From the phase difference between each antenna elements, our proposed phased array antenna has a sharp beam and beam steering characteristics.
This paper presents a design and fabrication of 4 × 4 one-sided directional slot array antenna on indium phosphide (InP) substrate for 0.3 THz (300 GHz) wireless link. The antenna has top antenna metal layer and bottom floating metal layer. Polyimide dielectric layer is stacked between each metal layer. The antenna is placed on the deep etched InP substrate. By optimizing the length of the bottom floating metal layer, one-sided directional radiation can be realized. The branched coplanar wave guide (CPW) transmission line is connected to each antenna element with the same electrical length. The size of the 4 × 4 array antenna is 2,730 μm x 3,000 μm with uni-traveling-carrier photodiodes, DC bias and ground lines. Simulated realized gain in peak direction of the proposed antenna is 11.7 dBi. The transmission measurement is carried and measured received power.
This paper presents a design and fabrication of 1 x 4 one-sided directional slot array antenna with director metal layer on indium phosphide (InP) substrate for 300 GHz wireless link. The floating metal and polyimide dielectric layer are stacked on InP. Antenna is designed on the top metal layer. By optimizing the length of the bottom floating metal layer, one-sided directional radiation can be realized. The branched coplanar wave guide (CPW) transmission line is connected to each antenna element with the same electrical length. The size of the 1 x 4 array antenna is 2,550 µm x 1,217 µm x 18 µm. In order to enhance the gain of forward direction, director metal layer is placed over 83 µm from top metal layer. Simulated realized gain in peak direction of our antenna is 9.23 dBi. The measured center frequency is almost the same as that of the simulation results.