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Design Of Integrated Circuits For Optical Communications

The terahertz (THz) antennas, which have features of small size, wide frequency bandwidth and high data rate, are important devices for transmitting and receiving THz electromagnetic waves in the emerging THz systems. However, most of THz antennas suffer from relatively high loss and low fabrication precision due to their small sizes in high frequency bands of THz waves. Therefore, this paper presents a detailed overview of the most recent research on the performance improvement of THz antennas. Firstly, the development of THz antennas is briefly reviewed and the basic design ideas of THz antennas are introduced. Then, THz antennas are categorized as metallic antennas, dielectric antennas and new material antennas. After that, the latest research progress in THz photoconductive antennas, THz horn antennas, THz lens antennas, THz microstrip antennas and THz on-chip antennas are discussed. In particular, the practical difficulties for the development of THz antennas are discussed with promising approaches. In addition, this paper also presents a short review of the process technology of THz antennas. Finally, the vital challenges and the future research directions for THz antennas are presented.

An overview of terahertz antennas

A multiple input-multiple output antenna assembly with high isolation between the antennas is disclosed. The antenna assembly includes a substrate with a ground layer at its surface. Two antennas are disposed opposing each other on the substrate. An isolation element in a form of a patterned slot is interposed between the first and second antennas on the ground plane. A first signal port is provided for applying a first signal to excite the first antenna and a second signal port is provided for applying a second signal to excite the second antenna. The isolation element provides isolation that inhibits electromagnetic propagation between the two antennas.

Wideband, high isolation two port antenna array for multiple input, multiple output handheld devices

This paper presents the results of a study on improving the performance parameters such as the impedance bandwidth, radiation gain and efficiency, as well as suppressing substrate loss of an innovative antenna for on-chip implementation for millimetre-wave and terahertz integrated-circuits. This was achieved by using the metamaterial and the substrate-integrated waveguide (SIW) technologies. The on-chip antenna structure comprises five alternating layers of metallization and silicon. An array of circular radiation patches with metamaterial-inspired crossed-shaped slots are etched on the top metallization layer below which is a silicon layer whose bottom surface is metalized to create a ground plane. Implemented in the silicon layer below is a cavity above which is no ground plane. Underneath this silicon layer is where an open-ended microstrip feedline is located which is used to excite the antenna. The feed mechanism is based on the coupling of the electromagnetic energy from the bottom silicon layer to the top circular patches through the cavity. To suppress surface waves and reduce substrate loss, the SIW concept is applied at the top silicon layer by implementing the metallic via holes at the periphery of the structure that connect the top layer to the ground plane. The proposed on-chip antenna has an average measured radiation gain and efficiency of 6.9 dBi and 53%, respectively, over its operational frequency range from 0.285–0.325 THz. The proposed on-chip antenna has dimensions of 1.35 × 1 × 0.06 mm3. The antenna is shown to be viable for applications in millimetre-waves and terahertz integrated-circuits.

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Study on on-Chip Antenna Design Based on Metamaterial-Inspired and Substrate-Integrated Waveguide Properties for Millimetre-Wave and THz Integrated-Circuit Applications

This letter deals with the design and implementation of modified serpentine structure (MSS) for isolation enhancement in microstrip antenna arrays. The antenna array is constructed using square patch radiators and is designed to operate at 2.45 GHz (ISM band) specially used for multiple-input-multiple-output (MIMO) communications. The proposed MSS acts like a band-reject filter to reduce the coupling between the radiators in the antenna array. The design and characterization of the modified serpentine structure is done, and its validity in MIMO scenario is verified through simulation and measurements. Experimental results show an isolation improvement of 34 dB for an array with reduced edge-to-edge spacing of 6 mm (λ0/20). The envelope correlation coefficient (ECC) is within the acceptable limit, making the solution viable for MIMO applications.

Deployment of Modified Serpentine Structure for Mutual Coupling Reduction in MIMO Antennas

A low-cost and high-gain on-chip terahertz (THz) dielectric resonator antenna (DRA) is proposed in this work. The DRA consists of a low-loss dielectric resonator (DR) made of high-resistivity silicon material and an on-chip feeding patch realized in a 0.18-μm CMOS technology for exciting the desired electromagnetic (EM) mode. The DR can be easily fabricated to the required dimension by wafer dicing of a 2-in silicon wafer. With a 500-μm thick DR, a higher order mode of TE δ, 1 , 7 can be excited, which greatly enhances the antenna gain. Such higher order mode operation also provides a reliable design. If a fundamental mode is selected, the DR thickness is around 100 μm at THz frequencies, which not only requires an additional wafer thinning process, but the wafer is also easily broken during the fabrication process. The feeding patch is used to excite the TE δ, 1 , 7 mode. Moreover, its ground plane also prevents the EM field from leaking into the lossy CMOS silicon substrate, which improves the antenna efficiency. The simulated antenna gain can be 7.9 dBi while providing radiation efficiency of 74% at 341 GHz with 7.3% bandwidth. To characterize the DRA performance, an identical CMOS imager is designed to be integrated with the proposed DRA and an on-chip patch antenna. By comparing the measured responsivity of these two imagers, the gain improvement of the DRA over the on-chip patch antenna can be obtained. Three samples are measured to evaluate the robustness of the proposed antenna over process variation. The measured results show that the maximum gain improvement of 6.7 dB can be acquired at 327 GHz. The proposed DRA with the integrated CMOS imager is also employed to successfully demonstrate a THz transmissive imaging system at 327 GHz. To the best of authors’ knowledge, this is first higher order mode DRA working at THz frequencies.

340-GHz Low-Cost and High-Gain On-Chip Higher Order Mode Dielectric Resonator Antenna for THz Applications

A single dielectric resonator antenna (DRA) capable of enhancing the antenna gain of each element of a $2\times 2$ terahertz (THz) antenna array realized in a 0.18- $\mu \text{m}$ CMOS technology is proposed in this paper. The DRA implemented in a low-cost integrated-passive-device technology is flip-chip packaged onto the CMOS antenna array chip through low-loss gold bumps. By designing the DRA to work at the higher order mode of TE $_{3,\delta,9}$ , only a single DRA, instead of conventionally needing four DRAs, is required to simultaneously improve the antenna gain of each element of the $2\times 2$ antenna array. This not only simplifies the assembly process, but it can also reduce the assembly cost. Moreover, the DRA can provide great antenna gain enhancement because of being made of high-resistivity silicon material and higher order mode operation. The simulated antenna gain of each on-chip patch antenna of the $2\times 2$ CMOS antenna array can be increased from 0.1 to 8.6 dBi at 339 GHz as the DRA is added. To characterize the proposed DRA, four identical power detectors (PDs) are designed and integrated with each element of the $2\times 2$ THz antenna array. By measuring the voltage responsivity of each PD output, the characteristics of each antenna of the antenna array with the proposed DRA, including the gain enhancement level and radiation pattern, can be acquired. The measurement results match well with the simulated ones, verifying the proposed DRA operation principle. The four PDs with the proposed DRA are also successfully employed to demonstrate a THz imaging system at 340 GHz. To the best of our knowledge, the proposed DRA is the one with the highest order operation mode at THz frequencies reported thus far.

Single Flip-Chip Packaged Dielectric Resonator Antenna for CMOS Terahertz Antenna Array Gain Enhancement

A flip-chip-assembled W-band receiver composed of a 90-nm CMOS chip and an integrated-passive-device (IPD) carrier is presented in this paper. The chip which integrates a low-noise amplifier, a single-sideband mixer, a frequency doubler (FD), and a wide-band variable-gain amplifier, is flip-chip packaged to the IPD carrier through a low-loss interconnect. The simulated loss of the interconnect without any compensation network is only 0.95 dB at 94 GHz. The FD can provide differential output without any additional lossy balun required, effectively increasing the FD output power, and hence relaxing the local oscillator generation circuit design. The experimental results show that the proposed packaged receiver can provide a variable gain from 11.3 to 48.2 dB, while having an input 1-dB compression point from −43.7 to −29 dBm as the RF frequency is 90 GHz. The intermediate bandwidth and minimum noise figure can be 1.0 GHz and 7.8 dB, respectively. The proposed receiver only consumes 73.9 mW from a 1.2-V supply. As compared with prior works, the proposed receiver exhibits higher gain, lower noise, and lower power dissipation even though a less-advanced 90-nm CMOS technology is adopted. To the best of the authors’ knowledge, this is the first W-band CMOS receiver assembled on an IPD carrier reported thus far.

A Flip-Chip-Assembled W-Band Receiver in 90-nm CMOS and IPD Technologies

A low-loss and low-cost terahertz (THz) substrate-integrated waveguide (SIW) and a SIW filter implemented in a commercially-available GaAs integrated-passive-devices (IPD) technology are proposed for THz applications. Ellipse vias penetrating through a 100- $\mu \text{m}$ thick GaAs substrate are employed to realize a low-loss SIW. The via’s orientation is designed as being transverse, instead of being longitudinal, to the propagation direction of the input wave, which can improve the insertion loss by 2.7 dB at 415 GHz due to lower signal leakage from the waveguide. The proposed SIW is able to provide simulated insertion loss of only 0.39 dB/mm, i.e., 0.14 dB/ $\lambda _{\mathrm {g}}$ , at 340 GHz. A new SIW filter structure using the ellipse vias is proposed which not only successfully realizes a low-loss fourth-order Chebyshev filter under hard design-rule-check (DRC) rules imposed by the IPD technology, but also can enhance out-of-band rejection by 10.5 dB at 390 GHz as compared with conventional waveguide filters. A slot-coupled coplanar waveguide (CPW) to SIW transition structure without any impedance tuning stub required is also proposed to measure the proposed SIW and SIW filter. The proposed transition structure can give simulated insertion loss of 0.7 dB at 340 GHz while keeping return loss better than 10 dB from 307 to 374 GHz. Eight samples are measured to demonstrate the robustness of the proposed designs against process variations. Experimental results show that the proposed transition structure with a 220- $\mu \text{m}$ long SIW and the SIW filter can provide measured insertion loss of 0.7 and 3.6 dB at 327.5 GHz, respectively. The reasons for the discrepancy between the simulation and measurement results are identified and discussed in detail. As compared with prior works, the proposed SIW and SIW filter exhibit lower loss, lower cost, higher repeatability, higher reliability, and mass-producible capability. To the best of the authors’ knowledge, this is the first demonstration of the THz SIW and THz SIW filter designs using a commercially-available and mass-producible IPD technology reported thus far.

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Low-Loss Low-Cost Substrate-Integrated Waveguide and Filter in GaAs IPD Technology for Terahertz Applications

In MIMO system, the effect of mutual coupling between the antennas influences and often deteriorates the transmission capacity of the wireless communications. In this paper, band-stop filters using spur-line and CPS structures between two antennas are proposed to reduced the effect of the coupling. Simulation and measurement show that more than 20dB isolation between antennas has been obtain in a 2.45 GHz MIMO system.

Te-Yen Chiu

Papers

340-GHz Low-Cost and High-Gain On-Chip Higher Order Mode Dielectric Resonator Antenna for THz Applications

Single Flip-Chip Packaged Dielectric Resonator Antenna for CMOS Terahertz Antenna Array Gain Enhancement

A Flip-Chip-Assembled W-Band Receiver in 90-nm CMOS and IPD Technologies

Low-Loss Low-Cost Substrate-Integrated Waveguide and Filter in GaAs IPD Technology for Terahertz Applications

Band-stop Filter Design of Coplanar Stripline