SUPPLEMENTARY MATERIAL
High-Frequency Thermal-Electrical Cycles for Pyroelectric Energy Conversion
Bikram Bhatia,1 Anoop R. Damodaran,2 Hanna Cho,3 Lane W. Martin,2,4 and William P. King1,2
1
Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign
2
Department of Materials Science and Engineering and Materials Research Laboratory,
University of Illinois Urbana-Champaign
3
4
Department of Mechanical Engineering, Texas Tech University
Department of Materials Science and Engineering, University of California, Berkeley
(S1) BaTiO3 film deposition and characterization
The 40 nm SrRuO3 / 150 nm BaTiO3 / 80 nm SrRuO3 heterostructures were deposited on
GdScO3 (110) substrates by pulsed-laser deposition employing a KrF excimer laser (wavelength
= 248nm) using BaTiO3 and SrRuO3 ceramic targets (Praxair Inc.). The BaTiO3 layer was
deposited at 600 C in 20 mTorr of oxygen, at laser repetition rates of 2 Hz and a laser fluence of
1.5 J/cm2. The SrRuO3 layer was deposited at 640 C in 100 mTorr of oxygen, at laser repetition
rates of 15 Hz and laser fluence of 1.4 J/cm2. Following growth, the films were cooled to room
temperature at an oxygen pressure of 760 Torr. X-ray diffraction image of the as-grown films
indicates single phase (00l) oriented films (Figure S1a). All measurements were performed on
the film in as-grown condition.
Figure S1. (a) X-ray diffraction pattern and (b) 5 µm×5 µm atomic force microscope image of
the 150 nm thick BaTiO3 film on SrRuO3/GdScO3 (110). The RMS roughness of the film was
0.67 nm.
(S2) Dielectric constant measurement versus Temperature
Figure S2 shows the BaTiO3 thin film dielectric constant (ε) and loss tangent (tanδ)
measured at temperatures 25 to 150 °C. The measurement was performed by mounting the
microfabricated heterostructure described in Figure 1 on a bulk heater stage. Agilent E4980A
precision LCR meter applied a sinusoidal excitation voltage of 50 mV at 1 kHz on the top
SrRuO3 electrode and the resulting current was measured from the bottom electrode. The
dielectric constant of the film increases with increasing temperature and tanδ is less than 0.1 for
the shown temperature range indicating that the Curie temperature is above 150 °C and electrical
leakage in the film is sufficiently low. The film Curie temperature, estimated by finding the xintercept of the extrapolated 1/ε, was about 400 °C.
Figure S2. BaTiO3 film dielectric constant and tanδ measured as a function of temperature using
an LCR meter with excitation amplitude of 5 mV and at 1 kHz.
(S3) Displacement-Electric field measurement
Figure S3 shows the equivalent circuit and results for the Displacement-Electric field
(D-E) measurements. A function generator applied a triangular voltage waveform with amplitude
7 V and frequencies 1 kHz and 10 kHz to the top SrRuO3 electrode. The current from the bottom
SrRuO3 electrode is fed to a current-to-voltage converter and the resulting signal is numerically
integrated to obtain the electric displacement change due to the out-of-plane electric field. No
electrical input was applied to the heater strip.
Figure S3. (a) Setup used to measure field-dependent film electric displacement using a currentvoltage converter. (b) D-E loops measured at 20 °C for frequencies 1 kHz and 10 kHz.
(S4) Pyroelectric-Electric field measurement
Figure S4 shows the equivalent circuit and results for pyroelectric measurement versus
electric field. A function generator applied a bipolar sinusoidal heating bias of amplitude 1 VRMS
across the length of the gold heater strip at frequencies 500 Hz and 1 kHz. In addition to heating,
an out-of-plane electric field was applied to the top SrRuO3 electrode to obtain the fielddependence of the pyroelectric response. The bias on the top electrode was varied linearly
between +7 and -7 V steadily at 0.1 Hz. The sinusoidal heating bias at angular frequency ω
changes the temperature at a frequency 2ω. This temperature change causes a pyroelectric
current that is measured from the bottom electrode using a lock-in amplifier. This phase-sensitive
2ω technique allows measurement of the electric displacement change only due to heating and
not the varying electric field.
Figure S4. (a) Setup used to measure field-dependent pyroelectric loops using a phase-sensitive
2ω method. (b) Pyroelectric loops measured at 20 °C for heating frequencies 1 and 2 kHz.