Molecular sensor based on virtual buried nanowire

A method of modifying a multi-gate field effect transistor usable for sensing at least one type of molecules in a gas or liquid sample and comprising:

• a) a piece of semiconductor with a first region extending between a source region and a drain region, and left and right lateral regions extending along the first region on different sides, the source region and drain region doped with dopants of a same sign, the left and right lateral regions doped with dopants of an opposite sign to the source and drain regions, and the first region doped with a dopant of the same sign as the source and drain regions;
• b) left and right lateral gate electrodes that respectively produce an electric field in the left and right lateral regions, creating a conducting channel in the first region when appropriate voltages are applied to them, a position of the conducting channel depending on the applied voltages;
• and
• c) a sensing surface adjacent to the first region, that molecules of the at least one type adhere to when the sensing surface is exposed to the molecules, the conductivity of the conducting channel being measurably affected by a local concentration of the adhering molecules near the position of the conducting channel;
• the method comprising heat treating the transistor under conditions such that some of the dopants from the left and right lateral regions diffuse into the first region, reducing an effective width of the first region by at least 30% at its narrowest point, but not reducing the effective width to zero at any point.