Terahertz (THz) range holds between infrared light and millimeter wave or microwave radiation. Moreover, THz waves is highly attenuated by the metal object or sensitive to an inter-molecular binding force. Therefore, imaging using THz range is attracted much attention for security, manufacturing, chemical imaging, and so on. In our research, the THz detector composed of Indium arsenide (InAs) high electron mobility transistor (HEMT) and one-sided directional slot antenna on a chip will be developed. In this paper, we focused on the antenna on a chip. The proposed antenna has three layers, namely, top antenna metal, dielectric substrate (BCB, benzocyclobutene) and bottom floating metal layer. There are a coplanar (CPW) feed lines and slots on the top antenna metal. By optimizing the size of the bottom floating metal layer, the radiation toward the back side is suppressed. The CPW feed line is connected the gate electrode on the InAs HEMT. In order to maximize the receiving THz signal form the antenna to InAs HEMT, antenna and gate input impedance is characterized by using the 3D electromagnetic simulator. It has been found that when the input impedance of the gate electrode changes from 10 ohms to 50 ohms, the voltage generated at the gate electrodes is tripled. The antenna was fabricated by the conventional photolithography process. The size of the radiation metal is 290 μm x 210 μm on the top metal with probe pads. The measured antenna gain is 5.57 dBi at 0.93 THz compared with the 5.96 dBi antenna gain at 1 THz from the simulation.
We report the low-temperature bonding of a lithium niobate (LiNbO3) chip with gold (Au) thin film to a silicon (Si)
substrate with patterned Au film for hybrid-integrated optical devices. The bonding was achieved by introducing the
surface activation by plasma irradiation into the flip-chip bonding process. After the Au thin film (thickness: 500 nm)
on the LiNbO3 chip (6 mm by 6 mm) and the patterned Au film (thickness: 2 μm) on the Si substrate (12 mm by 12 mm)
were cleaned by using argon (Ar) radio-frequency (RF) plasma, Au-Au bonding was carried out in ambient air with
applied static pressure (~50 kgf). The LiNbO3 chips were successfully bonded to the Si substrates at relatively low
temperature (< 100 °C). However, when the bonding temperature was increased to be greater than 150 °C, the LiNbO3
chips cracked during bonding. The tensile strength (calculated by dividing the total cross-sectional area of the initial,
undeformed micropatterns) of the interface was estimated to be about 70 MPa (bonding temperature: 100 °C). It was
sufficient for use in optical applications. These results show the potential for producing highly functional optical
devices and for low-cost packaging of LiNbO3 devices.
This paper describes the low-temperature bonding of a lithium niobate (LiNbO3) waveguide chip to a silicon (Si) substrate for integrated optical systems. The bonding was achieved by introducing the surface activation by plasma irradiation into the flip-chip bonding process. After the surfaces of the Au thin films (thickness: 100 nm) of the
LiNbO3 chip and the Si substrate were cleaned using an Ar radio frequency (RF) plasma, Au-Au bonding was carried out only by contact in ambient air with applied static pressure. The bonded chips fractured at bonding temperature higher than 150°C because of the coefficient of thermal expansion (CTE) mismatch. The LiNbO3 chips were successfully bonded to the Si substrates at relatively low temperature (100°C). The die-shear strength of the LiNbO3 chip was estimated to be more than 12 kg (3.8 MPa), the upper limit of our shear testing equipment.