Microelectromechanical systems (MEMS) and methods

A method of fabricating a distributed Bragg reflector, the reflector being at least partially reflective and at least partially transmissive for at least a wavelength of electromagnetic radiation;

• the method comprising:
• forming a first layer of a first material or material composition defining a bottom layer;
• forming a sacrificial layer on the bottom layer;
• forming a second layer of a second material or material composition defining a top layer on the sacrificial layer and a supporting structure connected to the bottom layer, the top layer comprising a membrane and an optical area of the same second material or material composition;
• and
• removing at least part of the sacrificial layer to form a cavity between the bottom layer and the top layer such that the supporting structure supports the top layer relative to the bottom layer and no further supporting structure is provided within the cavity,
• wherein after the at least part of the sacrificial layer is removed, at least the top layer comprising the membrane and the optical area has residual tensile stress,
• wherein the bottom and top layers of material, and the cavity, are a quarter of said wavelength in optical thickness.