Management and storage of energy converted via a pyroelectric heat engine

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

“…Thin‐film geometries can also enable fast thermal cycling, owing the fact that the volume of the active pyroelectric is small. As P = W · f , fast cycling also enables high power, as demonstrated with thin‐film devices fabricated with on‐chip heating elements, obtaining power densities of 3, 80, and 500 W cm −3 for barium titanate (BTO), PZT, and PMN‐PT films, respectively …”

“…The coupled response between electrical energy and thermal energy is a feature present in all ferroelectric materials arising primarily from the temperature dependence of the polarization state. These pyroelectric properties have been identified as the potential conversion mechanisms enabling waste‐heat scavenging, solid‐state cooling, and power‐beaming applications . Pyroelectric energy harvesting still largely relies on materials which are harmful to the environment, toxic, or not compatible with CMOS semiconductor manufacturing processes …”

“…Classical ferroelectrics such as PZT and BTO have pyroelectric coefficients ranging from –200 to –400 μC m −2 K −1 , electric breakdown fields from 100 to 200 kV cm −1 , and relatively high specific heat. Thus, thermal efficiencies of 0.3% are calculated from the parameters provided by Zhang for PZT and Bhatia for BTO . Polymeric pyroelectrics such as vinylidene fluoride‐trifluoroethylene (PVDF) have a lower pyroelectric coefficient, higher specific heat, and a large breakdown voltage, reaching efficiencies of 0.8%, which are calculated from published parameters .…”

“…To compare our experimental results to classic ferroelectric materials, we use the electrothermal coupling parameter found in the efficiency equation (Equation ) as a figure of merit, where only materials with demonstrated energy conversion and measured properties are considered. In Figure c, BTO, PZT, and PMN‐PT, harvestable energy densities per cycle are shown with respect to the electrothermal coupling parameter. For the area‐enhanced Si‐doped HfO 2 films examined in this work, we obtain a temperature‐normalized energy density of 0.15 μJ cm −2 K −1 and a coupling factor of 1.7 × 10 −3 .…”

“…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.…”