Thin PZT Film Pressure Microsensor
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Thin PZT Film Pressure Microsensor S.I. Khartsev, M.A. Grishin, Kenth Nilsson &, and A.M. Grishin KTH, Department of Microelectronics and Information Technology, S-164 40 Kista, SWEDEN; & Qenico AB, S-184 85 Åkersberga, SWEDEN.
ABSTRACT We report on a ferroelectric film pressure sensor fabricated on the top of 4 mm long and 1.4 mm in diameter Pt80Ir20 (PtIr) rod-shaped tip. It consists of a PZT(0.5µm)/LSMO(0.1µm) film heterostructure, deposited by pulsed laser ablation of stoichiometric ceramic targets PbZr0.52Ti0.48O3 and La0.67Sr0.33MnO3, and a circular, ∅ = 1.2 mm, Au electrode on the top of the PZT film. The Au/PZT/LSMO/PtIr thin-film capacitor demonstrates good ferroelectric properties: dielectric constant of 762 and loss tanδ =0.008 @ 5 kHz, induced polarization as high as 32 µC/cm2 at electric field of 250 kV/cm. Piezoelectric test, performed in a hydrostatic pressure chamber, exhibits the piezoelectric constant to be as high as 67 pC/N. This is 20% higher than 56 pC/N shown by a polarized bulk PZT sensor fabricated from the ceramics used as the target in the pulsed laser deposition process. Such an increase of the piezoelectric constant we attribute to the preferential (001) orientation of the PZT film grown on the PtIr bulk substrate. The resolution of the thin PZT film pressure microsensor was found to be about 1 mbar.
INTRODUCTION Nowadays the application of piezoelectric materials based on the lead zirconate titanate (PZT) ceramics is explosively emerging from the simple spark igniters and phonograph pick-ups to complex piezoelectric actuators and transformers, ultrasound motors, and microelectromechanical systems (MEMS) (see, for example [1, 2]). Ferroelectric ceramics is also well suited for pressure sensors since piezosensors do not require power supply and guarantee very high and accurate frequency response. [3] We report on a thin PZT film microsensor fabricated by pulsed laser deposition (PLD) technique on the head of a 1.4 mm in diameter platinum tip. The sensor demonstrates the piezoelectric response to hydrostatic pressure pulses to be as high as 67 pC/N.
EXPERIMENTAL DETAILS A brief description of the processing technique is as follows: a 248-nm KrF excimer laser (Lambda Physik-Compex 102) was used to ablate stoichiometric ceramic targets of the following compositions: La0.67Sr0.33MnO3 and PbZr0.52Ti0.48O3. Both layers were made at a laser radiation energy density of 2-3 J/cm2, a pulse repetition rate of 20 Hz, and a distance between target and substrate of 60 mm. The background pressure did not exceed 10 -6 Torr. Special precaution was undertaken to correctly measure temperature at the substrate surface. 4 mm long and 1.4 mm F8.12.1
Figure 1. Schematic view and the photo of the PZT thin-film pressure sensor. in diameter Pt80Ir20 (hereinafter PtIr) tips, shown in Fig.1, were used as substrates. LSMO and PZT films were deposited on the top of the nicely polished tip’s head in the on-axis PLD geometry. All the processing parameters are summarized and listed in Table I. The PZT/LSMO film proc
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