Pressure transducer with composite diaphragm

#The present invention generally relates to pressure transducers and, more particularly, to the diaphragm portions of such transducers.

#Pressure transducers that use piezoresistors are well known in the art. Generally, such transducers are formed with a silicon substrate and an epitaxial layer, which is grown on the substrate. A portion of the substrate is removed, leaving a thin, flexible diaphragm portion. The piezoresistors are located in the diaphragm portion to form a pressure transducer.

#In operation, at least one surface of the diaphragm is exposed to a process pressure. The diaphragm deflects according to the magnitude of the pressure, and this deflection bends the attached piezoresistors. Bending of the diaphragm creates changes in the resistance value of the piezoresistors, which is reflected as a change in the output voltage signal of a resistive bridge formed at least partially by the piezoresistors.

#The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.

#FIG. 1 is a bottom view of a diaphragm portion of the pressure transducer illustrating a preferred boss and batten structure.

#FIGS. 2A-2G illustrate various steps during the fabrication of the pressure transducer.

#It should be understood that the drawings are not necessarily to scale and that the embodiments are illustrated using graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. It should be understood, of course, that the invention is not necessarily limited to the particular embodiments illustrated herein.

#Referring initially to FIG. 1, a bottom view of a diaphragm 10 for a pressure transducer is shown. The diaphragm 10 includes a layer 12 of first diaphragm material formed in a solid square having a length “L” on each side. A second, patterned layer 14 of diaphragm material is attached to the first layer 12. As illustrated in FIG. 1, the second layer 14 comprises four bosses 16 interconnected by four battens 18. While the boss and batten structure shown in FIG. 1 is preferred, it will be appreciated that a variety of different patterns can be formed in accordance with the present invention. Piezoresistors 19 are attached to the second layer 14 at the base of each boss 16.

#To form the pressure transducer diaphragm 10 shown in FIG. 1, the steps depicted in FIGS. 2A-2G are followed. FIG. 2A shows the formation of a substrate 20 having a top surface 22 and a bottom surface 24. The substrate 20 can be formed in a variety of known manners and can comprise any one of a variety of known substrate materials. In the preferred embodiment, the substrate comprises single crystal silicon doped with a p-type material.