Tokyo, May 21, 2012 – Ricoh Company, Ltd. (President & CEO: Shiro Kondo) has succeeded in developing a unique ink-jet printing (IJP) technique that can produce PZT (lead zirconate titanate) (*1) in a voluntary pattern shape at 2μm-film thickness. The company demonstrated its functionality with an actuator (*2) created by this method. Further, Ricoh has simultaneously developed a lead-free piezoelectric material, bearing the same deformation properties as the PZT material on a silicon substrate. Both are world firsts. Combining both technologies will allow us to manufacture a lead-free piezoelectric device (*3), bearing functionality equivalent to PZT, on a silicon substrate using the IJP method at low cost and with low environmental impact.
The IJP method using ink-jet printing techniques in the manufacturing process of electronic devices has attracted much attention in recent years. It has many advantages over conventional semiconductor manufacturing processes. These include the efficient use of materials, fewer man-hours, reduced environmental impact, sharply reduced manufacturing costs, and the ability to respond to small-lot production of diverse products.
Ricoh has made PZT material, currently used extensively for piezoelectric elements, into an ink with a specific technology, and has succeeded in molding a piezoelectric pattern. The pattern demonstrates mechanical deformation properties as an actuator at 2μm film thickness. This thickness is about 50 times that of the film formed with the usual IJP method. This was not possible without the integration of technologies for controlling ink ejection in drawing precise patterns, modifying hydrophilicity and hydrophobicity (*4) of a substrate surface, and even, eliminating discards during firing thick film. Further, there are unique devisals on the nature of a solvent and drying speed control, which are needed to prepar film at a uniform thickness.
PZT has unique piezoelectric properties (*5) and ferroelectric properties. It is used in sensors or actuators such as car-navigation systems and high precision positioning devices. Although PZT contains lead, which is designated a controlled substance by the RoHS Directive (*6), PZT is exempted and often used, as there is no alternative material that matches its properties. Accordingly, although the development of lead-free materials is advancing in every direction, a practical-application level has not yet been reached.
With this project, Ricoh developed a material having about the same deformation properties (deformation amount when applied voltage) as PZT. It could be used to replace PZT. This was done in a system of materials (BSnT material) of lead-free barium titanate with tin added. This material needs to be fired at high temperature to form a high quality film. To do so, Ricoh raised the thermal stability of the under layer (electrode layer provided under the piezoelectric material) of the substrate and enabled film formation of BSnT with properties at a practical level on the silicon substrate. This enabled application as a microelectromechanical system (MEMS) and enabled modularization. The application area was significantly extended. Further, Ricoh has adopted a method to use the precursor of BSnT in liquid form, unlike the conventional powder method. Doing so allowed adoption of the IJP method to form piezoelectric film, resulting in cost and environmental advantages.
Surface morphology of the BSnT films fired at different temperatures.
(The one on the right fired at higher temperature shows larger grain size, indicating better film properties.)
Piezoelectric material has been used very broadly. We believe that combining these two technologies makes it possible to substitute the piezoelectric element of the conventional PZT, from both the material (lead-free material) and the manufacturing process (IJP method). It has both environmental and cost advantages. Ricoh will first manufacture a prototype of an actuator, then work on technical solutions, targeting commercialization.
In addition, Ricoh will announce both technologies at "The 29th Meeting on Ferroelectric Materials and Their Applications (FMA29)," a well-known conference, to be held in Kyoto May 23 to 26.