A thermal inkjet printhead with generally planar heater elements disposed
in respective bubble forming chambers, whereby the area of each heater is
less than 300 .mu.m.sup.2. The heater area influences the energy
required to heat the heater volume up to the fluid superheat limit; the
energy required to heat the protective coatings covering the heater to
the superheat limit; the heat that diffuses into the underlayer prior to
bubble nucleation; and, the heat that diffuses into the ink prior to
bubble nucleation. Reducing the surface area of the heater reduces all
of these terms and has a significant impact on the energy required to
form a bubble and eject ink.