Printable Interlinked ZnO Photodetectors and Sensors

Most ZnO-nanostructure devices are fabricated using time-consuming nanomanipulation or one-by-one fabrication techniques, making them unattractive for large-scale production. Despite advantages in manufacturing cost and scalability, solutions-based processing has not produced high performing ZnO thin-film devices. This novel solutions-based process produces ZnO devices with shorter response times, lower device biases, and high light sensitivity.

OVERVIEW:
A ZnO thin film is formed by iteratively printing zinc acetate dehydrate on an electrode channel or other substrate and subsequently curing at ~180oC for 10 minutes. The zinc acetate dehydrate decomposes to form uniform ZnO nanoparticles throughout the precursor film. This film is annealed at medium and high temperatures causing the nanoparticles to connect and form a ZnO thin film.

APPLICATIONS:
ZnO thin films are used in a variety of applications. The three most important current applications include as a conducting electrode in photovoltaics, as a luminescent material in light emitting diodes, and as a gas sensor for different types of gases.

HOW IT WORKS:
Curing zinc acetate dehydrate at 180oC for 10 minutes produces particles ranging from 15 to 35 nm in diameter. Because these particles are comparable in size to the Debye length for ZnO, 19 nm, the resulting film has greater responsivity to changes in light intensity. The medium temperature annealing enables self-assembly of the ZnO nanoparticles into a thin-film, and the short term, high temperature annealing improves its surface properties.

BENEFITS:
These innovations in processing produce ZnO thin films with shorter responsivity to changes in light intensity (by a factor of 5-15 times), and reduced bias voltages (by a factor of 3-20 times). These ZnO thin films also show high light sensitivity (Ilight:Idark = ~300,000).

WHY IS IT BETTER:
This invention allows deposition using printing techniques of ZnO thin films on a variety of substrates. The resulting films have high sensitivity, substantially improved responsivity to changes in light intensity, and require bias voltages in ranges widely used in electronics. Consequently, this innovation allows broader adoption of low cost, highly scalable solutions-based techniques in the production of ZnO thin films.

OTHER APPLICATIONS:
Because of the low toxicity and biodegradability for ZnO, ZnO thin films have potential biological applications such as biomedical imaging, drug delivery, gene delivery, and sensing of a wide array of molecules of medical relevance.