, and a perspective, Mandelis Perspective Related Article(s): [Rev. Sci. Instrum.82, 120901 (Year: 2011)]
, discussing this have been published.
The Sawyer-Tower bridge. In its original form, it did not take into account the presence of the leakage current represented here as Rs. This current can be partially balanced by introducing a shunt resistor Rb.
Two saw-tooth time-voltage profiles with frequencies differing by 5%.
Example of the dynamic time ramping technique used to measure the pyroelectric coefficient of a 67%Pb(Mg1/3Nb2/3)O3-33%PbTiO3 single crystal from Ref. 35. A Peltier element run at 1 mHz (≈16 min 40 s period) was used to create the saw-tooth temperature profile with amplitude of 1 degree. Reproduced with permission.
(a) Scheme of the setup for the basic Chynoweth method; (b) example of the pyroelectric current measured with the Chynoweth technique. The sample is 0.2 × 0.2 μm wide, 0.4 μm thick self-supported film of BaTiO3 tethered to a Si substrate.36 The top and the bottom contacts are of Ag and account for more than 90% of the heat loss. The inset shows a full period (laser on and off, 666 Hz); the main panel shows an exponential fit. The film was irradiated by an IR laser (λ = 1310 nm) with a flux of 3 mW/mm2. Note: for a self-supported film, a lump model is applicable and the heating and the cooling processes are fully symmetric (Appendix A 2 b).
(a) The setup for the temperature ramping technique. The pyroelectric materials can be represented as a current generator with equivalent current given by I(t) = Aα∂T/∂t where A is the area of the contact and α is the pyroelectric coefficient. The measurement device can be a high impedance voltmeter, electrometer, or a low impedance nanoammeter (or current to voltage converter) for the short circuit measurement mode (Appendix A 1 b); (b) equivalent electrical scheme of a pyroelectric material and a high-impedance voltmeter.
(a) Pyroelectric current generated in the layered structure: Ag/quasi-amorphous pyroelectric SrTiO3/Si in response to periodic (1 kHz) irradiation with an IR (1310 nm) laser.44 The combined thickness of the Ag contact and SrTiO3 layer is <0.5 μm. Therefore, after a few tens of μsec, the current is determined by the thermal diffusion into the thick (250 μm) substrate. Note: the heating and the cooling currents are distinctively different; (b) fitting of the “heating” current to the diffusion equation.
Pyroelectric current generated in a 0.5 mm thick crystal of LiTaO3 mounted on a copper plate and irradiated by an IR laser modulated at 57 Hz. The diameter of the crystal is 8 mm, absorbed radiation density is 0.4 mW/mm2. Increasing the cooling part of the cycle by a factor of three (frequency will drop by half) makes the current upon heating constant to within ≈1%.
(a) The instrumentation diagram for the continuous temperature oscillation technique; (b) equivalent electrical circuit with the pyroelectric material and a high-impedance voltmeter connected in parallel.
(a) Typical frequency dependence of pyroelectric current generated in response to sinusoidally modulated heating when the lumped model is applicable; the bold line shows the idealized case when a current-to-voltage converter has a very small impedance over all frequency ranges. At sufficiently high frequencies ( ≫ 1), the pyroelectric current remains constant I max = A · α · F/G. In practical measurements, above some frequency the input impedance of the current-to-voltage converter increases sufficiently to cause a decrease in the measured current (shown as a dashed line). The actual pyroelectric currents are known to remain constant into the nanosecond time scale. The inset shows that at very low frequencies, the current is directly proportional to frequency. (b) Typical frequency dependence of the pyroelectric voltage.
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