Bio-based Piezoelectric Energy Generator

Seung-Wuk Lee (UCB) and Ramamoorthy Ramesh (UCB)

We have fabricated mechanical energy scavenging device made from biopiezoelectric viruses, by exploiting the naturally aligned dipole structure of a bacterial virus, M13 phage. We enhanced the phages’ piezoelectric properties through chemical and physical structural modifications and successfully demonstrated that a phage-based piezoelectric device could produce up to 6 nA and 400 mV. One potential area that might benefit from this approach is the energy harvesting or other transducer applications at a miniature scale, especially those that need to be integrated into small devices. Since they can be easily mass-amplified and genetically tuned, phage-based piezoelectric materials present an adaptable and cost-effective means of harvesting energy from the environment and is an important step toward accessing the largely untapped potential of piezoelectric biomaterials.

Mechanical Energy Scavenging Device Made from Piezoelectric Viruses. (a) Actual virus-based piezoelectric energy scavenging device. (b) Schematic of device shown in (a).

Direct-Write Polymeric Piezoelectric Nanogenerator

Liwei Lin (UC Berkeley)

Mechanical energy scavenging from ambient environments is an attractive renewable source of energy for various applications. In pursuing these mechanical energy harvesters, especially for small-scale applications, one fundamental issue is the design and selection of structural materials for efficient conversion of mechanical energy into electricity. We have developed polymeric nanogenerators based on organic piezoelectric nanofibers, meaning when they are compressed, a voltage is built up across the polymer nanofiber. These nanofibers are made of highly flexible polyvinylidene fluoride (PVDF), which minimizes resistance to external mechanical movements in low frequency, large-deflection energy scavenging applications. We utilize a direct-write technique to produce and place piezoelectric PVDF nanofibers on working substrates. This technique could allow systems to satisfy their power needs by harnessing the vibration energy around them.

Vibrational Energy Scavenging

In the Ramesh group, in collaboration with Wright’s groups, we have used polarization force microscopy (PFM) to image the as-grown domain pattern at the highly strained, clamped end of the piezoelectric bender while electromagnetically driving its deflection at the free end. We have verified that crisp images can be captured while rastering the scanning probe across the flexible cantilever. High-quality, epitaxial PZT films have been created via PLD as verified by x-ray diffraction (XRD) and PFM measurements. The sol-gel process has produced thick (>500 nm) PZT films, which show a piezoelectric response (~30 pC/N) considerably less than the epitaxial films. XRD confirms that these films—while possibly favorably textured—are composed of randomly oriented grains, ~200-300 nm wide as measured by PFM.

The next major challenge is to fabricate the cantilevers without damaging the active PZT layer. The current process consists of selectively removing the bulk of the silicon beneath the cantilevered region using a silicon nitride hard mask and SF6 plasma etch. The cantilevers are then released by anisotropically etching through the film stack with an ion mill. Effort is also being placed into optimizing the anneal steps of the sol-gel process to improve the texture of the PZT grains and thereby increasing the piezoresponse.