A colorimeter has an absorber for absorbing radiation energy and converting the radiation energy into thermal energy. A resistor is connected to the absorber for converting thermal energy into an electrical signal. A membrane is connected to the resistor for controlling a thermal discharge from the resistor. A substrate is connected to the membrane and has a tri-layer structure comprised of an etching layer having a preselected thickness, an etching stop layer and a support substrate. The membrane is spaced-apart from a main surface of the etching stop layer by the preselected thickness of the etching layer.