Piezoelectric ink jet head

A piezoelectric ink jet head comprising a plate-shaped substrate with a plurality of recesses that form pressure chambers to be filled with ink and are separated by partition walls, which are part of the substrate, being formed in the direction of substrate surface on one side of the substrate, while nozzles for discharging the ink contained in the pressure chambers in the form of droplets are disposed so as to communicate with the respective recesses via nozzle passages, and a common feed path is disposed to communicate via a feed port with the recesses for supplying the ink to the pressure chambers, the substrate being provided, on the surface thereof where the recesses are formed, with a drive section comprising:

• a piezoelectric element made in a thin plate of transverse vibration mode;
• an oscillator plate that closes the recesses so as to form the pressure chambers and oscillates as the piezoelectric element deforms thereby to decrease the volume of some of the pressure chambers and discharge the ink from the pressure chamber through the nozzle in the form of droplet;
• and
• upper and lower electrodes that sandwich the piezoelectric element on the upper and lower sides, wherein the oscillator plate is formed to cover a plurality of dot forming sections and the piezoelectric element is formed the same size as the oscillator plate;
• the partition wall that separates adjacent recesses has such a cross sectional shape as the width W1 in the planar direction at the upper end on the side of the substrate where the drive section is formed and height H in the direction of the substrate thickness satisfy the expression (1):
• W1≧H (1)
• while the width W1 and width W2 of the lower end at the bottom of the recess of the substrate in the planar direction satisfy the expression (2):
• W1≦W2 (2).