Jang-Yong Kim

Na0.5K0.5NbO3 film microwave varactors

Na0.5K0.5NbO3 (NKN) and Pb(Zr0.53Ti0.47)O3 (PZT) films have been grown by rf-magnetron sputtering and pulsed laser deposition techniques, correspondingly, on sapphire (Al2O3-0112, r-cut), quartz (Y+36°-cut) and YAlO3 + 1% Nd (Nd:YAlO3-001) single crystal substrates with Interdigital Capacitor (IDC) of Coplanar Waveguide (CPW) structure. Photolithography and metal lift-off technique was used for processing of the tunable microwave capacitor. Microwave network analyzer with G-S-G Picoprobe and probe station performed microwave measurement with external DC bias. NKN film interdigital capacitors on Nd:YAlO3 show superior performance in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40 V, 200 kV/cm) was about 29%, loss tangent ∼ 0.13, K-factor from 152% @10 GHz to 46% @40 GHz, voltage independent C p was about 230 fF, tan δ p changes from 0.14 @10 GHz to 0.36 @40 GHz, real and imaginary part of interconnect impedance increases with frequency from 0.13 Ω @10 GHz to 0.50 Ω @40 GHz and from 1.9 Ω @10 GHz to 5.9 Ω @40 GHz respectively.

Processing and On-Wafer Measurements of Ferroelectric Interdigitated Tunable Microwave Capacitors

Na0.5K0.5NbO3 (NKN) and Pb(Zr0.53Ti0.47)O-3 (PZT) films have been grown by rf-magnetron sputtering and pulsed laser deposition techniques, correspondingly, on sapphire (Al2O3-0112, r-cut), YAlO3 + 1% Nd (Nd:YAlPO3-001), and quartz (Y+36degrees-cut) single crystal substrates. Interdigital capacitor (IDC) of coplanar waveguide (CPW) structures were defined by a standard lift off technique in a Au(0.5mum)/Cr(10nm) electrode electron beam evaporated on ferroelectric film surface. IDCs consisted of five pairs of fingers separated by 2 and 4 mum gap. On-wafer microwave characterization was performed using a workbench equipped with a coplanar probe station (Cascade Microtech) with G-S-G (Ground-Signal-Ground) Picoprobe, a network analyzer (Agilent Technologies E8364A) operating in 45 MHz to 40 GHz range and programmable power supply for de DUT (Device Under Test) biasing. Assumed equivalent circuit for the IDC/CPW structure contains planar capacitor under test C, the coplanar line with a complex impedance sigma and a parasitic capacitance C, between the signal and ground lines. The de-embedding technique has been employed to determine all six complex parameters C, sigma and C-p from S-parameter measurements performed for three different device structures: device, open and thru. NKN film interdigital capacitors on sapphire show superior performance in this microwave range: the frequency dispersion was as low as 18%, voltage tunability = 1 - C(40V)/C(0) (40 V, 200 kV/cm) about 14%, loss tangent similar to0.11, K-factor = tunability/tandelta from 131% @ 10 GHz: to 56% @ 40 GHz. The reliability of the de-embedding procedure is clearly proved by analysis of the frequency dependences of the parasitic capacitance and loss tangent as well as impedance of the coplanar line. Within the accuracy of experimental data and de-embedding calculations these values appear to be voltage independent: C-p similar to 70 fF, tan delta(p) changes from 0.07 @ 10 GHz to 0.15 @ 40 GHz; real and imaginary part of interconnect impedance increases with frequency from 0.16 Omega @ 10 GHz to 0.36 Omega @ 40 GHz and from 1.6 Omega @ 10 GHz to 5.84 Omega @ 40 GHz respectively.

Buried Tantalate-Niobate Microwave Varactors

We present characteristics of microwave variable capacitors (varactors) buried in 2.5 mum thick AgTa0.5Nb0.5O3 (ATN) film pulsed laser deposited on sapphire single crystal. 2 mum gap interdigital capacitors (IDC) were fabricated by photolithographic, dry etching and lift-off processes. For comparison, similar IDCs were also defined on top of ATN film. Capacitance and loss tangent have been determined using a modified de-embedding technique in the microwave range 25 MHz -40 GHz. Buried structures show higher values of capacitance and tunability, keeping the same level of losses compared to standard topped devices and resulting in an increased K-factor = tunability/tan delta. Experimental results are explained within equivalent circuit model. Besides the increased performance, the new design avoids the need of a successive planarization step, which could be required in an integration process.

Microwave Properties of AgTa 0.5 Nb 0.5 O 3 Thin Film Varactors on Various Substrates

AgTa_0.5Nb_0.5O₃ (ATN) 400 nm thick films have been sintered by pulsed laser deposition technique on LaAIO₃ (001), sapphire (Al₂O₃-011_2, r-cut) single crystal substrates and Corning 7059 glass. Photolithography and metal lift-off technique were used to fabricate tunable coplanar waveguide interdigital capacitors (CPWIDCs). On-wafer test of varactors was performed with microwave network analyzer and G-S-G microwave probe. ATN/LaAIO₃ capacitors demonstrated the highest tunability (~5.8%@20GHz), ATN/Glass showed the best flat dispersion (-3.9%) and ATN/ AI₂O₃ showed the lowest loss tangent (~0.06@20GHz) in the microwave range from 1 to 40 GHz.