High nozzle density printhead ejecting low drop volumes

1. A printhead assembly for an inkjet printer, the printhead assembly comprising:

a printhead substrate having a plurality of drop generators formed thereon at an area density of at least six drop generators per square millimeter, wherein at least one of the plurality of drop generators emit droplets having a drop volume of about 1 pico liter; and,

a fluid source providing fluid to the drop generators, the fluid having a viscosity in the range of 0.7 to 15 centipoise at a temperature of 25° C.

2. A printhead assembly according to claim 1 wherein each of the plurality of drop generators has a chamber for holding a quantity of ink and a nozzle in fluid communication with the chamber.

3. A printhead assembly according to claim 2 wherein the nozzle is circular and has a radius of between 5.3 and 5.7 microns.

4. A printhead assembly according to claim 1 wherein each of the plurality of drop generators has an actuator for emitting the droplets, each of the actuators having a thermo-mechanical structure for converting an electrical drive pulse into kinetic energy within the ink droplets.

5. A printhead assembly according to claim 4 wherein the thermo-mechanical structure has a cantilevered lever with a paddle secured to its free end, the lever using differential thermal expansion to bend the paddle toward the nozzle for emitting the droplet.

6. A printhead assembly according to claim 4 wherein the droplets emitted from the drop generators remove heat generated by actuation of the thermo-mechanical structures.