Patent ID: 7857427

Claim:
An inkjet printhead comprising: a plurality of nozzles; a bubble forming chamber corresponding to each of the nozzles respectively so that each nozzle is disposed in a roof of the respective chamber, the bubble forming chambers containing ejectable ink; a dielectric layer bonded to the roof of the respective chamber; a generally planar heater element disposed in each of the bubble forming chambers respectively, the heater element being bonded on one side to the dielectric layer so that the other side faces into the chamber from the roof of the chamber, the heater element being configured for receiving an energizing pulse to heat some of the ejectable ink above its boiling point to form a gas bubble on the side facing into the chamber, whereby the gas bubble causes the ejection of a drop of the ejectable ink from the nozzle; a MEMS fluid sensor for detecting the presence or otherwise of the ejectable ink in the chamber, the MEMS fluid sensor having a MEMS sensing element formed of conductive material having a resistance that is a function of temperature, the MEMS sensing element having electrical contacts for connection to an electrical power source for heating the sensing element with an electrical signal; and control circuitry for measuring current passing through the sensing element during heating of the sensing element, the control circuitry being configured to determine the temperature of the sensing element from a known applied voltage, the measured current and a known relationship between the current, resistance and temperature, wherein the dielectric layer has a thermal product less than 1495 Jm −2 K −1 s −1/2 , the thermal product being (ρCk) 1/2 , where ρ is the density of the layer, C is specific heat of the layer and k is thermal conductivity of the layer.