Electroacoustic transducer of the so-called "electret" type, and a method of making such a transducer

Claim 1

A method of making an electroacoustic transducer characterized by the steps of forming a mask on one main face of a wafer of monocrystalline silicon, said mask having a pattern defining the peripheral contour of the recessed portion and the place of any membrane supporting projections thereon of a plurality of transducer units contiguous with one another in rows and columns; etching the silicon accessible through said mask away to a pre-determined depth, using an etching agent, to form the recessed portion of said transducer units; forming on the peripheral edges, which are raised relatively to the recessed portions, a mask whose pattern defines the outer circumferential contour of each of the transducer units contiguous with one another in rows and columns, and forming on the other main face of the wafer a mask whose pattern defines all the openings extending through the substrate of the transducer units to be made from the wafer; etching the silicon accessible through said two masks away by using an etching agent, so that, on the one hand, a mesh-like lattice pattern of V-shaped grooves is recessed in the raised peripheral edges, and on the other, openings extending through the substrate are formed, said openings being covered by masking material on the side where said mesh-like lattice pattern is provided; removing the masking material; covering the assembly thus obtained with a layer of dielectric, in particular a layer of SiO 2 ; charging said layer of dielectric uniformly with electric charge; covering the assembly on the side where said mesh-like lattice pattern is provided with a membrane foil; covering the openings extending through the wafer, except those extending through said edge portions; filling the exposed openings from the side away from that where the membrane foil is provided with an adhesive so as to secure the membrane foil to the substrate through said adhesive; providing on the membrane foil electrodes and contacts for contacting with electronics for the transducer units by means of a shadow mask; cutting the membrane foil according to the mesh-like lattice pattern of V-shaped grooves; and disintegrating the wafer according to said pattern of V-shaped grooves to form a plurality of separate transducer units.

Claim 2

A method of making an electroacoustic transducer characterized by the steps of forming a mask on one main face of a wafer of monocrystalline silicon, said mask having a pattern defining the peripheral contour of the recessed portion and the place of any membrane supporting projections thereon of a plurality of transducer units contiguous with one another in rows and columns; etching the silicon accessible through said mask away to a pre-determined depth, using an etching agent, to form the recessed portion of said transducer units; forming on the peripheral edges, which are raised relatively to the recessed portions, a mask whose pattern defines the outer circumferential contour of each of the transducer units contiguous with one another in rows and columns, and forming on the other main face of the wafer a mask whose pattern defines all the openings extending through the substrate of the transducer units to be made from the wafer; etching the silicon accessible through said two masks away by using an etching agent, so that, on the one hand, a mesh-like lattice pattern of V-shaped grooves is recessed in the raised peripheral edges, and on the other, openings extending through the substrate are formed, said openings being covered by masking material on the side where said mesh-like lattice pattern is provided; removing the masking material; covering the assembly thus obtained with a layer of dielectric, in particular a layer of SiO 2 ; charging said layer of dielectric uniformly with electric charge; covering the assembly on the side where said mesh-like lattice pattern is provided with a membrane foil; covering the openings extending through the wafer, except those extending through said edge portions; filling the exposed openings from the side away from that where the membrane foil is provided with an adhesive so as to secure the membrane foil to the substrate through said adhesive; providing on the membrane foil electrodes and contacts for contacting with electronics for the transducer units by means of a shadow mask; cutting the membrane foil according to the mesh-like lattice pattern of V-shaped grooves; and disintegrating the wafer according to said pattern of V-shaped grooves to form a plurality of separate transducer units.

Claim 3

A method of making an electroacoustic transducer characterized by the steps of forming a mask on one main face of a wafer of monocrystalline silicon, said mask having a pattern defining the peripheral contour of the recessed portion and the place of any membrane supporting projections thereon of a plurality of transducer units contiguous with one another in rows and columns; etching the silicon accessible through said mask away to a pre-determined depth, using an etching agent, to form the recessed portion of said transducer units; forming on the peripheral edges, which are raised relatively to the recessed portion, a mask whose pattern defines the outer circumferential contour of each of the plurality of transducer units contiguous with one another in rows and columns, and forming on the other main face of the wafer a mask whose pattern defines all the openings extending through the substrate of the transducer units to be made from the wafer; etching the silicon accessible through said two masks away by using an etching agent, so that, on the one hand, a mesh-like lattice pattern of V-shaped grooves is recessed in the raised peripheral edges, and on the other, openings extending through the substrate are formed, said openings being covered by masking material on the side where said mesh-like lattice pattern is provided; removing the masking material; covering the assembly thus obtained with a layer of dielectric, in particular a layer of SiO 2 ; via the exposed openings, and from the side on which the membrane foil is provided, evaporating or sputtering a material on to the interior of said openings and on the opposed portions of the membrane foil, so as to secure the membrane foil through said material to the substrate; providing on the membrane foil electrodes and contacts for contacting with electronics for the transducer units by means of a shadow mask; cutting the membrane foil according to the mesh-like pattern of V-shaped grooves; and disintegrating the wafer according to said pattern of V-shaped grooves to form a plurality of separate transducer units.

Claim 4

A method of making an electroacoustic transducer characterized by the steps of forming a mask on one main face of a wafer of monocrystalline silicon, said mask having a pattern defining the peripheral contour of the recessed portion and the place of any membrane supporting projections thereon of a plurality of transducer units contiguous with one another in rows and columns; etching the silicon accessible through said mask away to a pre-determined depth, using an etching agent, to form the recessed portion of said transducer units; forming on the peripheral edges, which are raised relatively to the recessed portion, a mask whose pattern defines the outer circumferential contour of each of the plurality of transducer units contiguous with one another in rows and columns, and forming on the other main face of the wafer a mask whose pattern defines all the openings extending through the substrate of the transducer units to be made from the wafer; etching the silicon accessible through said two masks away by using an etching agent, so that, on the one hand, a mesh-like lattice pattern of V-shaped grooves is recessed in the raised peripheral edges, and on the other, openings extending through the substrate are formed, said openings being covered by masking material on the side where said mesh-like lattice pattern is provided; removing the masking material; covering the assembly thus obtained with a layer of dielectric, in particular a layer of SiO 2 ; via the exposed openings, and from the side on which the membrane foil is provided, evaporating or sputtering a material on to the interior of said openings and on the opposed portions of the membrane foil, so as to secure the membrane foil through said material to the substrate; providing on the membrane foil electrodes and contacts for contacting with electronics for the transducer units by means of a shadow mask; cutting the membrane foil according to the mesh-like pattern of V-shaped grooves; and disintegrating the wafer according to said pattern of V-shaped grooves to form a plurality of separate transducer units.