Ki-Byoung Kim

High-tunability and low-microwave-loss Ba0.6Sr0.4TiO3 thin films grown on high-resistivity Si substrates using TiO2 buffer layers

In this Letter, we report on high-tunability and low-microwave-loss properties of Ba0.6Sr0.4TiO3 (BST) thin films by use of atomic-layer-deposited TiO2 films as the microwave buffer layer between BST and high-resistivity Si substrate. The interdigital capacitor fabricated on BST films grown on TiO2∕high resistivity Si (2kΩcm) substrates showed the much enhanced tunability value of 33.2% while retaining an appropriate Q factor, as compared to the tunability values of BST (21%) films grown on MgO single-crystal substrates and BST (8.2%) films grown on TiO2∕normal Si (10Ωcm) substrates. The coplanar waveguide BST phase shifter fabricated on TiO2∕high resistivity Si exhibited a phase shift of 95° and insertion loss of 3.09 dB at 15 GHz and an applied voltage of 50 V. ALD-grown TiO2 buffer layers enable the successful integration of BST-based microwave tunable devices onto high-resistivity Si wafers.

Ku-band transition between microstrip and substrate integrated waveguide (SIW)

In this paper, a Ku-band planar transition between microstrip and substrate integrated waveguide at satellite communication band is discussed. The SIW is one of alternatives for packaging the microwave components on the same substrate. The transition structure suggested in this paper shows the insertion loss of 0.7 dB at 12 GHz including transmission line of full wavelength.

Iris waveguide bandpass filter using substrate integrated waveguide (SIW) for satellite communication

In this paper, an iris waveguide filter with substrate integrated waveguide (SIW) structure at satellite communication band is discussed. The SIW structure is realized by via-holes on the substrate and shows a possibility of integration with other circuits. The iris waveguide filter has the insertion loss of 3.36 dB, the return loss of about 20 dB, and bandwidth of 3 %. Also, the iris waveguide filter using SIW has a sharp skirt characteristic.

Coplanar ferroelectric phase shifter on silicon substrate with TiO/sub 2/ buffer layer

In this paper, a BST coplanar phase shifter with differential phase shift of 98/spl deg/ at 50 V and FoM of 46.7/spl deg//dB has been realized. The potential feasibility of integrating BST films into Si substrate as microwave phase shifter and/or coplanar waveguide tunable devices with TiO/sub 2/ thin film buffer layer has been successfully demonstrated. TiO/sub 2/ as buffer layer has been successfully grown onto Si substrate by ALD (atomic layer deposition).

Ferroelectric Thin-Film-Based Electrically Tunable Bandpass Filters

We report on gold/Ba 0 . 5 Sr 0 . 5 TiO 3 (BST) ferroelectric thin film C-band tunable bandpass filters (BPFs) designed and fabricated on magnesium oxide substrates using three different structures: microstrip, coplanar waveguide (CPW), and conductor backed coplanar waveguide (CBCPW). The two-pole filters were designed for a center frequency of 5.89, 5.88, or 5.69 GHz with bandwidths of 3, 9, or 7%, respectively. The BST-based CPW filter offers a higher sensitivity parameter as well as a lower loss parameter compared to the BST tunable two-pole microstrip filter and CBCPW filter. With an applied voltage of 40 V, the tuning range for the BPF with CPW structure was determined to be 170 MHz.

Design of Tunable Band-pass Filters and Phase Shifters Using BST Thin Film

In this paper, the band-pass filters (BPFs) and phase shifters using BST thin film are presented. Filters are consisted of Microstrip, Coplanar Waveguide (CPW), and conductor backed CPW (CBCPW) structures and phase shifters are consisted of CPW line and CPW with slit structures to improve phase shift effect. From the measurement results, the Microstrip, CPW, and CBCPW bandpass filters show the center frequencies of 6.61 GHz, 6.31 GHz, and 6.21 GHz with the insertion losses of 7.33 dB, 5.83 dB, and 6.83 dB, respectively at the bias voltage of 40 V. The tuning range for the bandpass filters is determined as 3%~8%. From the experiments, the CPW line and the CPW with slit phase shifters show the insertion losses of 1.9 dB and 2.4 dB at the bias voltage of 30 and the phase shifts of 9.8° and 10.6° at 16 ~ 18 GHz, respectively.

Millimeter Wave Compact Branch Line Coupler Using Metal–Air–Metal Capacitors

In this paper, a compact branch line coupler fabricated on a GaAs substrate using surface micromachining. It is composed of a dielectric-supported air-gapped microstrip line (DAML) structure, which is a low-loss transmission line with an air-post and is useful for integration with other micro electro-mechanical system (MEMS) and/or MMIC components. The size reduction of the branch line coupler is accomplished by the insertion of metal–air–metal (MAM) capacitors within the structure. The coupler shows an isolation characteristic of approximately 21 dB and differences in magnitude and phase of less than 0.3 dB and 2°, respectively.

Influence of narrow transverse slit in ferroelectric based voltage tunable phase shifter

We report on gold/Ba0.5Sr0.5TiO3 (BST) ferroelectric thin film Ku-band phase shifters designed and fabricated on MgO substrates using two different structures; the coplanar waveguide (CPW) meander line phase shifter and the new phase shifter with narrow transverse slits in the ground plane of the CPW structure. The ability of these devices to provide a variable phase shift is based on the change in dielectric constant of BST with an applied dc bias. The phase shifter with narrow transverse slits showed larger phase shift capability than that of the conventional meander line phase shifter. In the former phase shifter, the phase shift of about 10.6 as a maximum value for the frequency range from 16 GHz to 18 GHz was obtained. In the latter, the phase shift of 9.7 deg at 18 GHz and at an applied voltage of 30 V was measured.

New Tunable Microwave Ba0.6Sr0.4TiO3/MgO Phase Shifters Using Interdigital Capacitors and Slit-Inductors

In this paper, we report on the role of slit-inductors in notably improving phase shifting capabilities in Ba0.6Sr0.4TiO3 (BST) tunable phase shifters utilizing interdigital capacitor (IDC) structure. The IDC-based coplanar waveguide (CPW) phase shifter with slit-inductors fabricated on (100) oriented BST films deposited on MgO substrates exhibits a much enhanced phase difference of 35.52°, as compared to that (25.23°) of the IDC-based phase shifter at 12 GHz. The figure of merit (FoM) of the IDC-based phase shifters with slit-inductors shows larger value of 43.60°/dB as a result of improving phase shifting while retaining an appropriate insertion loss compared to that (35.67°/dB) of the IDC-based phase shifter without slit-inductor. This work demonstrates potential use of slit-inductors for producing high-performance CPW based BST tunable elements in microwave circuit.

Investigation on size reduction of a branch-line power divider using shunt-stub

This paper presents the size-reduced branch-line power divider using shunt-stub. By the equivalent circuits of quarter wavelength transmission line, each line of the branch-line divider is defined as the specific impedance value and the electric length of shunt-stub is given as a function of impedance of shunt-stub. It is shown that the bandwidth of the divider is decreased with decreasing size and/or increasing electric length of the shunt-stub. In spite of narrow band, these size-reduced branch-line power dividers using shunt-stub can be applied to a wireless-LAN system.