Re‐engineering the Polymer Capacitor, Layer by Layer

Abstract

be achieved at relatively lower fi elds. [ 3 ] However, this would require the design and the synthesis of new dielectric materials with higher relative permittivity and very low dielectric losses. In addition, because the energy density is proportional to E 2 , it would benefi t by charging the capacitor with as high of an electric fi eld as possible.Another approach, then, would be to use materials with higher barrier heights or electrodes with carefully selected work functions to minimize or retard the tunneling current, so that high energy densities, by charging the capacitors at high fi elds, can be achieved, without increasing the leakage current or reducing the effi ciency. But, again, this would require synthesis of new materials.We propose a novel approach to achieve higher energy densities by re-engineering the architecture of capacitors. Our new capacitor device is a layered structure that incorporates thin electron and hole blocking layers deposited between the conducting electrodes and the dielectric material as schematically illustrated in Figure 1 . [ 4 ] The purpose of these blocking layers is to achieve an "effective" increase in barrier height that will minimize or delay tunneling current until extremely high electric fi elds are reached, without the need to develop new dielectric materials. To explain our concept, let us fi rst restate Zhang and co-workers' observations in terms of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) levels. [ 3 ] Applying a positive bias voltage to the electron side of the capacitor raises the work function of the conducting electrode on the electron side, W fe . This reduces the energy gap ( E g ) between W fe and the LUMO level of the capacitor dielectric, thus reducing the barrier height. The higher the applied voltage, the smaller the E g , which in turn increases the fl ow of electrons over the barrier height or LUMO level of the capacitor dielectric. The insertion of an electron blocking layer (EBL), between the electrode and the dielectric fi lm, with a higher LUMO level than the capacitor dielectric ( Figures 1 and 2 ), Electrostatic capacitors offer high power density, lower loss, and higher operating voltage than their electrolytic and supercapacitor counterparts. However, these capacitors suffer from the low energy density (<2 J cm −3 ), limiting their applications in high power integrated systems such as pulsed power and high frequency inverters.In an electrostatic capacitor, the energy stored is in the form of an energy density in an electric fi eld. [ 1,2 ] Consequently, for linear dielectrics under an electric fi eld (dielectric constant independent of the applied fi eld), the stored energy density is linearly proportional to the dielectric constant ( ε ) and quadratically proportional to the applied electric fi eld ( E ). The level of the electric fi eld that can be applied, short of the catastrophic electrical failure (dielectric fi eld strength) of the material, may depend on either the inherent pro...

Improved dielectric permittivity and retained low loss in layer-structured films via controlling interfaces

“…In recent years, enormous attention and research enthusiasm have been devoted to high dielectric (high-k) materials for their wide applications in actuators [1,2], antennas [3], capacitors [4][5][6][7], wave-transparent (or absorbing) devices [8][9][10][11][12][13], and other electronic devices [14][15][16][17][18][19][20][21][22]. Most conventional highk materials are ceramic or ceramic composites, but their applications are seriously restricted by their intrinsic frangibility, high density, poor plasticity, and low breakdown strength.…”

CaTiO3 linear dielectric ceramics with greatly enhanced dielectric strength and energy storage density

“…Dielectric capacitors, which store energy electrostatically, are widely used in pulsed power systems and modern electronics due to the high power density. However, the low energy storage density of dielectric capacitors no longer meets the rising demand for compact, low cost and reliable devices, which limits their further applications . The energy in a dielectric capacitor is stored in the form of electric field and the corresponding energy storage density can be expressed by , where E is the electric field strength and D is the electric displacement within dielectric materials .…”

“…On the other hand, Joyce et al. have demonstrated that a proper thin film can act as electron or hole blocking layer in the polymer capacitor under high electric field, and thereby increase the dielectric strength . Considering alumina thin film generally has a very high dielectric strength, it is a challenge issue to further improve the dielectric strength of CaTiO 3 ceramics by introducing the alumina blocking layer between the electrodes and CaTiO 3 .…”

Ba‐based complex perovskite ceramics with superior energy storage characteristics

“…Introducing insulating blocking layers has been reported as an effective approach to further enhance the energy storage density 33,34 . As shown in the inset of Figure 6A, alumina has been sputtered between Ba(Mg 1/3 Nb 2/3 )O 3 ceramics and the electrodes.…”

“…In addition, it has been reported that the insulating thin films deposited between the conducting electrodes and the dielectric material can work as the electron or hole blocking layers, which successfully increase the dielectric strength in the polymer and glass capacitors 33,34 . Recently, Zhou et al have demonstrated that the dielectric strength in ceramics can also be further increased with the help of amorphous alumina thin films as the blocking layers 13 .…”