Sample well fabrication techniques and structures for integrated sensor

A method of forming an integrated device, the method comprising:

• forming a sample well within a cladding layer of a substrate;
• forming a sacrificial spacer layer over the substrate and into the sample well;
• performing a directional etch of the sacrificial spacer layer so as to form a sacrificial sidewall spacer on sidewalls of the sample well;
• forming, over the substrate and into the sample well, a functional layer that comprises at least one functional moiety and provides a location for attachment of a biomolecule, wherein functional material of the functional layer bonds to sacrificial spacer material of the sacrificial spacer layer;
• and
• after forming the functional layer, removing completely the sacrificial spacer material thereby removing the functional material bonded to the sacrificial spacer material, resulting in the functional layer disposed only on a bottom surface of the sample well.