Microwave power dependent properties of ferroelectric varactors

Pär Rundqvist
Department of Microtechnology and Nanoscience, Chalmers University of Technology, Sweden

Andrei Vorobiev
Department of Microtechnology and Nanoscience, Chalmers University of Technology, Sweden

Spartak Gevorgian
Department of Microtechnology and Nanoscience, Chalmers University of Technology, Sweden \ Microwave and High Speed Electronics Research Center, Ericsson AB, Sweden

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Ingår i: GigaHertz 2003. Proceedings from the Seventh Symposium

Linköping Electronic Conference Proceedings 8:68, s.

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Publicerad: 2003-11-06


ISSN: 1650-3686 (tryckt), 1650-3740 (online)


Ferroelectrics; especially in paraelectric phase; are widely considered for microwave applications. The main feature; that’s makes them attractive for tuneable microwave applications; is the DC field non-linear dependent dielectric permittivity. A large number of tuneable microwave devices and systems have been demonstrated in the past; In general; the microwave power dependence of film parameters is an undesirable effect; however when properly designed; ferroelectric components may be used in harmonic generators and mixers. In this work we report preliminary results of nonlinearity measurements of parallel-plate ferroelectric varactors integrated on Si wafers.

The first reports on experimental investigation of nonlinearities in BaxSr1-xTiO3 based ceramics date back to 1950s and early 1960s. DiDomenico et al report the first successful demonstration of a 3rd harmonic generator in 1962. Recently 2nd harmonic generation was demonstrated [4]; by applying DC bias. Samoilova et al. reported frequency conversion (harmonic generation) experiment in a Coplanar Waveguide (CPW) with a ferroelectric film. Where as Booth et al [6] uses a CPW with Ba0.3Sr0.7TiO3 film; the non-linear capacitance C by using two approaches: i) third harmonic generation; and ii) C(VDC) measurements at microwave frequencies. It was shown that the non-linear capacitance C determined from C(VDC) measurements is in excellent agreement with the one found from third harmonic generation experiment; this leads to the conclusion that ferroelectric devices might be tuned with nanosecond speeds.

To study nonlinearities Kozyrev et al designed a resonator loaded by a ferroelectric capacitor; using both a single signal as well as intermediation distortion; which confirmed previous results. Kozyrev et al also gives a simple theory for estimation of overheating of the ferroelectrics films at high power levels; and it was shown that the power handling capability of a ferroelectric tuneable filter may be as high as 3.5 W. Experiments and more detailed analysis of the microwave heating on nonlinearities are given elsewhere.

In this work; we used simple; on-chip microprobe reflection measurements to determine microwave power dependence of the capacitance of parallel-plate ferroelectric varactors. It is shown that the nonlinear parameters estimated from this experiment are in good agreement with the nonlinear parameters found from C(VDC) measurements at low frequencies. Hence; nonlinear parameters found from simple C(VDC) measurements may be used in the development of microwave devices; such as harmonic generators and mixers.


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6. J. C. Booth; R. H. Ono; I. Takeuchi; and K. S. Chang; “Microwave frequency tuning and harmonic generation in ferroelectric thin film transmission lines”; Appl. Phys Lett.; Vol. 84; pp. 718-720; 2002.

7. T. B. Samoilva; and K. F Astaf’ev; “Effect of Heat on the Nonlinearity of Plane Strontium Titanate Film Capacitor on Sapphire in a Microwave Field”; Technical Physics; Vol. 45; No 6; pp.759-765; 2000.

8. P. Rundqvist; A. Vorobiev; S. Gevorgian “Non-destructive microwave characterisation of Ferroelectric films on conductive substrates” submitted to integrated ferroelectrics.

9. A. K. Tagantsev; V. O. Sherman; K. F. Astafiev; J. Venkatesh and N. Setter; to be published in Journal of Electroceramics.

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