Three dimensional NAND devices with air gap or low-k core

A monolithic three dimensional NAND string device, comprising:

• a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate, wherein the semiconductor channel comprises a hollow body surrounding a middle region;
• at least one of an air gap or a low-k insulating material having a dielectric constant of less than 3.9 located in the middle region;
• a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprise at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level;
• a blocking dielectric located in contact with the plurality of control gate electrodes;
• at least one charge storage region located in contact with the blocking dielectric;
• and
• a tunnel dielectric located between the at least one charge storage region and the semiconductor channel.