US Patent 7176903 Piezoelectric element and touch screen utilizing the same

A piezoelectric element includes a substrate, a lower electrode on the substrate, a piezoelectric layer on the lower electrode, and an upper electrode on the piezoelectric layer. The upper electrode includes a common base and a plurality of parallel branches extending from the base. The branches are arranged at a regular interval or pitch λ1. The lower electrode faces the branches of the upper electrode via the piezoelectric layer. The thickness h of the piezoelectric layer and the branch pitch λ1 are determined to satisfy an inequality 0.005≦h/λ1≦0.1. The lower electrode has a hillock occurrence rate which is no greater than 0.1%.