NOVELTY - Fabrication of microfluidic device chips (50) comprises fabricating micromachined tubes (52) in a device wafer formed of semiconductor material; bonding the surface of device wafer to a first surface of second wafer to form a device wafer stack; bonding the second surface of second wafer to a first surface of metallic wafer to form a package wafer stack so that through-holes (30) in metallic wafer are individually fluidically coupled with through-holes of second wafer and define ports at second surface of metallic wafer; and singulating microfluidic device chips from package wafer stack.    USE - Fabrication of microfluidic device chips consisting of Coriolis mass flow sensors, density sensors, specific gravity sensors, fuel cell concentration meters, chemical concentration sensors, temperature sensors, drug infusion devices, fluid delivery devices, gas delivery devices, gas sensors, bio sensors, or medical sensors (claimed).    ADVANTAGE - The use of metallic package substrate in microfluidic device chip allows for elimination of any organic materials within the fluid flow path through the microfluidic device chips. By eliminating organic materials, a wider variety of fluids can be flowed through the device chips, including low or high pH liquids, high-temperature fluids, corrosive fluids, biofluids, solvents, and other fluids that tend to be incompatible with plastics and other organic materials due to potential corrosion, contamination, biocompatibility issues and the risk of out-gassing, melting or decomposition of organic materials. The wafer-level attachment of metallic package substrate enables high volume production applications to lower manufacturing costs of wide variety of microfluidic devices.    DETAILED DESCRIPTION - Fabrication of microfluidic device chips (50) comprises:    (A) fabricating micromachined tubes (52) in a device wafer formed of semiconductor material, where micromachined tubes are fabricated so that each micromachined tube has an internal fluidic passage and inlet and outlet defined in a surface of device wafer;    (B) bonding the surface of device wafer to a first surface of second wafer to form a device wafer stack and so that through-holes (24) in second wafer are individually fluidically coupled with inlets and outlets of micromachined tubes and define openings at second surface of second wafer;    (C) bonding the second surface of second wafer to a first surface of metallic wafer to form a package wafer stack so that through-holes (30) in metallic wafer are individually fluidically coupled with through-holes of second wafer and define ports at second surface of metallic wafer; and    (D) singulating microfluidic device chips from package wafer stack, each of microfluidic device chips comprising a package substrate formed by a singulated portion of metallic wafer, singulated portion of second wafer, singulated portion (36) of device wafer, one of micromachined tubes, package inlet and package outlet port defined by a pair of ports at second surface of metallic wafer, and continuous flow path between package inlet and outlet; and defined by, in series, one of through-holes in metallic wafer, one of through-holes in second wafer, inlet, passage and outlet of micromachined tube, second of through-holes in second wafer, and second of through-holes of metallic wafer.    The second wafer is formed of a glass-type inorganic amorphous solid. The metallic wafer is formed of an iron-nickel alloy, iron-nickel-cobalt alloy, nickel-based superalloy, titanium alloy, tungsten alloy, molybdenum alloy or stainless steel alloy.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of processing steps carried out to produce microfluidic device chips.    Through-hole in second wafer (24)    Through-hole in metallic wafer (30)    Singulated portion of device wafer (36)    Microfluidic device chip (50)    Micromachined tube (52)