Piezo-stack with passivation, and a method for the passivation of a piezo-stack

1. A piezo stack, comprising:

a plurality of side surfaces including opposing first and second side surfaces and opposing third and fourth side surfaces perpendicular to the first and second side surfaces, and

a first passivation layer applied on the first side surface,

wherein the first passivation layer has a rectangular cross section defining a pair of opposing ends that are flush with the opposing third and fourth side surfaces of the piezo stack, and the first passivation layer has a depth measured perpendicular to the first side surface,

a third passivation layer applied on the third side surface of the piezo stack perpendicular to the first and second side surfaces,

wherein the third passivation layer extends perpendicular to the first passivation layer and extends to the full depth of the first passivation layer, and

wherein the first passivation layer and the third passivation layer comprise different materials.

2. The piezo stack of claim 1 , comprising a second passivation layer applied on the second side surface opposite the first side surface,

wherein the second passivation layer has a rectangular cross section defining a pair of opposing ends that are flush with the opposing third and fourth side surfaces of the piezo stack.

3. The piezo stack of claim 2 , wherein at least one of the first and second passivation layers comprises plastic.

4. The piezo stack of claim 3 , wherein the plastic comprises a polyimide.

5. A method for the passivation of at least one side surface of a piezo stack, the method comprising:

providing a piezo block including opposing first and second side surfaces having a block length in a first direction, applying a first passivation layer on the first side surface of the piezo block,

curing the first passivation layer,

mechanically separating the piezo block to define at least one piezo stack having a stack length in the first direction that is less than the block length.

6. The method of claim 5 , further comprising applying a second passivation layer on the second side surface of the piezo block before the mechanical separation of the piezo block.

7. The method of claim 6 , wherein at least one of the first and second passivation layer is applied by a dispensing, template printing, or screen printing process.

8. The method of claim 6 , comprising curing the second passivation layer before the mechanical separation of the piezo block.

9. The method of claim 5 , wherein the mechanical separation of the piezo block is performed along one or more separating axes extending perpendicular to the first and second side surfaces.

10. The method of claim 5 , further comprising:

for one or more of the at least one piezo stack formed by the mechanical separation:

applying a third fourth passivation layer on a third side surface of the respective piezo stack, the third side surface extending perpendicular to the first and second surfaces,

wherein the third passivation layer extends perpendicular to the first passivation layer of the respective piezo stack and extends beyond the first and second edges of the third side surface in a direction perpendicular to the first passivation layer.