Frequency domain analysis of pyroelectric response in silicon-doped hafnium oxide (HfO2) thin films

Abstract

The pyroelectric response of polycrystalline, Si-doped HfO2 layers with a thickness of 20 nm is investigated in a frequency range of 2 Hz to 20 kHz. Local Joule heating of the pyroelectric material by a deposited nickel strip is used to achieve fast thermal cycles. Over the whole frequency range, a distinct pyroelectric response is registered. A pyroelectric coefficient of −72 μC/m2K is obtained at a frequency of 10 Hz, which is in good agreement with earlier low-frequency measurements. The pyroelectric current is evaluated with respect to electric field cycling, where a successive increase is observed during wake-up. By comparing measurement results in the low- and high-frequency limit, primary and secondary pyroelectric coefficients of −53 μC/m2K and −19 μC/m2K are estimated, respectively. Si-doped HfO2 is a promising material for future energy harvesting and IR sensor applications due to environmental friendliness and CMOS compatible manufacturing.

Pyroelectric Energy Conversion in Doped Hafnium Oxide (HfO2) Thin Films on Area‐Enhanced Substrates

“…For the field‐cycled sample, a large pyroelectric coefficient of −(1442 ± 10) μC m −2 K −1 is obtained at 0 V with respect to device footprint, which corresponds to a planar value of –74 μC m −2 K −1 with an area enhancement factor of 19.5. This is similar to earlier measurements with planar samples and a similar manufacturing technique, indicating a successful vertical integration of the pyroelectric Si‐doped HfO 2 films. At increasing voltages, the pyroelectric response decreases slightly, reaching −(1042 ± 23) μC m −2 K −1 at 3 V. The phase of the total current is displayed in Figure f, indicating values close to the ideal value of ±90°, proving the pyroelectric origin of the registered current.…”

“…Characterization of the pyroelectric effect in Si‐doped HfO 2 revealed the potential of this material system for energy conversion applications, with published pyroelectric coefficients of –84 and –46 μC m −2 K −1 . Recent reports showed that the pyroelectric coefficient remains stable in a temperature range from 20 to 160 °C and for rapid temperature cycles up to 20 kHz . Deep‐etched silicon structures have formed the basis of high‐surface‐area capacitors for energy storage applications and high‐density ferroelectric memory .…”

“…The temperature change imparted on the Si‐doped HfO 2 film is assumed to be uniform for testing. As the characteristic length of heat diffusion is much larger than the dimensions of the nanostructure, nonlinear effects are not expected but may arise in the kHz frequency range, where a lower temperature change might be realized in the bottom of the trench structures.…”

“…As the harvestable power density is proportional to cycle frequency, the current implementation with TiN electrodes is ultimately limited by the electrical resistance of the electrodes of up to 50 kΩ. In future implementations with highly conductive electrodes and optimized interfaces, the power output may be increased by orders of magnitude, as the pyroelectric effect in doped HfO 2 has already been demonstrated in the kHz regime . Practical implementation of pyroelectric energy harvesting or power beaming has been discussed in the literature, suggesting efficient electric energy extraction by circuit self‐synchronizing to the heat source using a pyroelectric sensor as a trigger signal.…”

Piezoelectric Response of Polycrystalline Silicon‐Doped Hafnium Oxide Thin Films Determined by Rapid Temperature Cycles

“…A SiO 2 layer with a thickness of 30 nm was used to electrically insulate the MFM stack from the overlapping 100 nm Ni film, which served as a resistive heater with a resistance of 13 Ohm. Further details of deposition and test structure manufacturing are reported elsewhere 28. Samples were mounted on a printed circuit board using electrically conductive silver glue and wire bonding.…”