In recent years, with the growing concerns over environmental protection and human health, environment-friendly materials have received increasing attention, and for decades researchers have been fiercely studying lead-free piezoelectric materials with high piezoelectric properties.

After more than 7-years of innovative research, Professor PAN Feng and his group from Key Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, presented a new type of environment-friendly piezoelectric material with giant piezoresponse and simple structure, small-ion-doped ZnO. They also provided a general rule describing the impact of doping on the piezoresponse of ZnO films.

Specifically, if doped ions substitute at Zn2+ sites, doping ZnO with small/big ions can enhance/reduce the piezoresponse. This rule is a useful guide in fabricating enhanced piezoresponse in wurtzite materials and offers a new paradigm to seek environment-friendly piezoelectric materials with high piezoelectric properties.

Their work, titled "Giant piezoresponse and promising application of environmental friendly small-ion-doped ZnO", was published in SCIENCE CHINA Technological Sciences.2012, Vol 55(2).

Piezoelectric materials are key materials for the fabrication of various transducers, pressure sensors and actuators, piezoelectric oscillator and actuators, transformer, surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices, which are widely used in the fields of information, energy, machinery, electronics, national defense, among others.

Because of their excellent piezoelectric property, lead (Pb)-based piezoelectric materials is one of the most widely exploited and extensively used piezoelectric materials. However, Pb is highly toxic and its toxicity can be further enhanced due to its easy volatilization during processing. Thus, processing and use of Pb-based piezoelectric materials can contaminate environments and damage human health, thereby limiting their applications.

With the rise in environmental awareness, lead-free piezoelectric materials have received greater attention, the prevailing trend being that environment-friendly lead-free piezoelectric materials will replace Pb-based piezoelectric materials.

As a piezoelectric material, ZnO has various advantages. Firstly, it has the strongest piezoelectric response among the tetrahedrally-bonded semiconductors. Secondly, it is structurally simple and easy to fabricate.

Moreover, ZnO films are compatible with semiconductor processes, and therefore has been widely used as sensors and actuators in micro-electromechanical systems and as SAW and BAW devices in the field of communications. However, performance improvements in piezoelectric devices demand significant piezoelectric behavior and stronger piezoresponse; in that regard d33 is the important parameter for evaluating piezoelectric property in ZnO.

See the article: Pan F, Luo J T, Yang Y C, et al. Giant piezoresponse and promising application of environmental friendly small-ion-doped ZnO. SCI CHINA Tech Sci, 2012, 55(2):1.