Ejection head for aggressive liquids manufactured by anodic bonding

• US 6,780,340 B2
• Filed: 11/26/2002
• Issued: 08/24/2004
• Est. Priority Date: 05/29/2000
• Status: Expired due to Term

• Current Assignee: Sicpa Holding SA
• Original Assignee: Olivetti Tecnost SpA (Telecom Italia S.p.A.)
• Inventors: Conta, Renato
• Primary Examiner(s): Hassanzadeh, P.
• Assistant Examiner(s): CULBERT, ROBERTS P
• Application Number:
  US10/296,629
• Publication Number:
  US 20030131475A1
• Time in Patent Office: 637 Days
• Field of Search: 216/27, 298/901, 438/21, 347/20, 347/22, 347/29, 347/44, 347/47, 347/54, 347/55, 347/56, 347/63, 347/64, 347/65, 347/67, 347/68, 347/71, 347/74, 347/75
• US Class Current: 216/27
• CPC Class Codes: B41J 2/16 Production of nozzles
• CPC Class Codes: B41J 2/1623 bonding and adhesion
• CPC Class Codes: B41J 2/1628 dry etching
• CPC Class Codes: B41J 2/1629 wet etching
• CPC Class Codes: B41J 2/1631 photolithography
• CPC Class Codes: B41J 2/1635 dividing the wafer into individual chips
• CPC Class Codes: B41J 2/1646 thin film formation by sputtering
• CPC Class Codes: F02M 51/06 Injectors peculiar thereto with means directly operating the valve needle
• CPC Class Codes: F02M 51/0603 using piezoelectric or magnetostrictive operating means
• CPC Class Codes: F02M 53/06 with fuel-heating means, e.g. for vaporising
• CPC Class Codes: F02M 61/1853 Orifice plates
• CPC Class Codes: Y10T 29/49401 Fluid pattern dispersing device making, e.g., ink jet

Abstract

A method for manufacturing an ejection head (10) or ejector suitable for ejecting in the form of droplets (16) a liquid (14) conveyed inside the ejection head (10), comprising a step of producing, from a silicon wafer, a nozzle plate (12) having at least one ejection nozzle (13); a step of producing, from another silicon wafer, a substrate (11) having at least one actuator (15) for activating the ejection of the droplets of liquid through the nozzle (13); and a step of joining the nozzle plate (12) and the substrate (11) together to form the ejection head, wherein this joining step comprises the production of a junction (25), made by means of the anodic bonding technology, between the substrate (11) and the nozzle plate (12), in such a way that, in the area of this junction (25), the ejection head (10) does not present structural discontinuities, and also possesses a resistance to chemical corrosion by the liquid (14) contained in the ejection head (10) at least equal to that of the silicon constituting both the substrate (11) and the nozzle plate (12). The method of the invention may be applied for manufacturing an ink jet printhead (110), having one or more nozzles (113a, 113b, etc.), which has the advantage, with respect to the known printheads, of also being suitable for working with special inks characterized by high level chemical aggressiveness. In general, the ejection head of the invention, thanks to its structure which is globally highly robust and also chemically inert in the area of the junction (25), can be used advantageously with various types of liquids, even with marked chemical aggressiveness, in different sectors of the art, for example for ejecting paints on various types of media, generally not paper, in the industrial marking sector; or for ejecting in a controlled way droplets of fuel, such as petrol, in an internal combustion engine.

Claims

1. Method for manufacturing an ejection head (10;

110), or ejector, suitable for ejecting a liquid (14;

140) in the form of droplets (16), and possessing internally a hydraulic circuit (21;

121) for containing and conveying said liquid (14;

140), comprising the following phases;

producing a nozzle plate (12;

112) having at least one ejection nozzle (13;

113a, 113b, 113c);

producing a substrate (11;

111) or actuation support having at least one actuator (15;

115a, 115b, 115c) for activating the ejection of said droplets (16) of liquid through said at least one nozzle (13;

113a, 113b, 113c); and

integrally joining said nozzle plate (12;

112) and said substrate (11;

111) together to form said ejection head (10;

110) and the relative hydraulic circuit (21;

121), this joining phase comprising the production by means of the so-called “

anodic bonding”

technology of a junction (25;

125), between said nozzle plate (12;

112) and said substrate (11;

111), arranged for being wetted by said liquid (14;

140) contained in the hydraulic circuit (25;

125),

wherein the phase of producing said nozzle plate (12;

112) includes the following steps;

providing a plate or wafer (51) made of silicon,

selectively removing the silicon of said plate (51) down a given depth, so as to form, along a face (51a) of said plate, a recess (54) defining a chamber (20) of said hydraulic circuit (21), and

forming, by means of an etching process and along a bottom (61) of said recess (54), said at least one ejection nozzle (13),

wherein the phase of producing said substrate (11;

111) includes the following steps;

providing a plate of wafer (70, 71) made of silicon,

forming, on an outer surface of said plate (11), said at least one actuator (15) and the tracks (72) for the electrical connection of it,

depositing a first protective layer (76) on said at least one actuator (15),

depositing a second protective and conductive layer (77) over said first protective layer (76), said second conductive layer (77) being arranged in the area of said at least one actuator (15) and in the junction zone where said substrate (11) will be joined together with said nozzle plate (12), and moreover forming a portion (77a) which extends, along said substrate (11), outside said junction zone,

depositing a preliminary layer of glass (78) on said conductive protection layer (77), said preliminary layer having the purpose of preparing said substrate (11) for being joined with said nozzle plate (12) by means of said anodic banding technology, and

subsequently etching said layer of glass (78) to uncover the zone of said actuator (15) and to define the junction areas (78a) between said substrate (11) and said nozzle plate (12),

and wherein the joining phase includes the following steps;

positioning into reciprocal contact said nozzle plate (12;

112) of silicon and said substrate (11;

111), in correspondence of said layer of glass (78), in such a way to arrange exactly said at least one nozzle (13;

113a, 113b, 113c) in front of said at least one actuator (15;

115a, 115b, 115c), and

affecting said junction (25) between said nozzle plate (12) and said substrate (11) by connecting said nozzle plate (12) and said portion (77a) of said conductive layer (77) respectively to a first (81) and a second counter-electrode (82) of an appropriate anodic bonding machine (85), and then applying by means of said machine (85) a determined voltage between said counter-electrodes (81, 82), said first counter-electrode (81) being formed of a plate which rests on said nozzle plate (12) along the side bearing said ejection nozzle (13) and acts as the anode during the production of said junction (25), whereas said second counter-electrode (82) acts as the cathode,

whereby a structural cohesion is obtained between the two surfaces of silicon and of glass (78), in reciprocal contact, respectively of said nozzle plate (12) and of said substrate (11).

2. Method for manufacturing an ejection head according to claim 1, wherein said preliminary layer is made of borosilicate glass (78).

3. Method for manufacturing an ejection head according to claim 2, wherein said layer of borosilicate glass (78) is made of a material known as Pyrex containing sodium.

4. Method for manufacturing an ejection head according to claim 1, wherein the phase of producing said substrate (11) comprises a step of planarization (CMP) to planarize said layer of glass (78) on the free surface intended for coupling with said nozzle plate (12), said step of planarization having the task of ensuring a high degree of planarity on said free surface for allowing said layer of glass (78) to interface and couple at contact with said nozzle plate (12).

5. Method for manufacturing an ejection head according to claim 1, wherein, during the phase of joining said substrate (11) and said nozzle plate (12) by means of said anodic bonding technology, said substrate (11) is maintained at a pre-established temperature by means of a heating element (83).

6. Method for manufacturing an ejection head according to claim 1, wherein said actuator (15;

115a, 115b, 115c) is of the thermal type and in particular is made of a resistor (74) which is suitable for rapidly heating in order to generate, within said liquid (14;

140), a vapour bubble suitable to cause the ejection of said droplets, and wherein said conductive protection layer (77;

177) in made of tantalum (Ta).

7. Method for manufacturing an ink jet printhead (110) possessing internally a hydraulic circuit (121) for containing and conveying ink (140), comprising the following phases:

producing a nozzle plate (112) having at least one ejection nozzle (113a, 113b,

producing a substrate (111) having at least one actuator (115a, 115b, 115c) for activating the ejection of said ink (140), in droplet form, through said at least one nozzle (113a, 113b, 113c); and

integrally joining said nozzle plate (112) and said substrate (111) together to form said printhead (110) and the relative hydraulic circuit (121), said joining phase comprising the production of a junction (125), between said nozzle plate (112) and said substrate (111), arranged for being wetted by the ink (140) contained in the hydraulic circuit (121),

wherein the phase of producing said nozzle plate (112) comprises the following steps;

providing a plate or wafer made of silicon;

selectively removing the silicon of said plate down a given depth, so as to form, along a face of said plate, a recess defining a chamber of said hydraulic circuit (121); and

forming, by means of an etching process and along a bottom of said recess, said at least one ejection nozzle (113a, 113b, 113c);

wherein the phase of producing said substrate (111) comprises the following steps;

providing a plate or wafer made of silicon;

forming, on a face of said plate, said at least one actuator (115a, 115b, 115c) and the tracks for the electrical connection of it;

depositing a first protective layer of silicon nitride and of silicon carbide on said at least one actuator,

depositing a second protective and conductive layer (177) of tantalum over said first protective layer of silicon nitride and of silicon carbide, said second conductive layer (177) of tantalum being arranged in the area of said at least one actuator and in the junction zone where said nozzle in plate (112) and said substrate (111) will joined together,

depositing a continuous layer of borosilicate glass (178) over said second layer (177) of tantalum,

selectively etching said continuous layer of borosilicate glass (178) in such a way that it extends only over said junction zone, and

planarizing (CMP) the free surface of said layer of borosilicate glass (178), so as to ensure a high degree of planarity of said surface adapted for the successive junction phase of said substrate (111) with said nozzle plate (112),

and wherein the phase of joining said substrate (111) and said nozzle plate (112) comprises the following steps;

positioning into reciprocal contact said nozzle plate (112) and said substrate (111), in correspondence of a said layer of borosilicate glass (78), in such a way to face exactly said at least one nozzle (113a, 113b, 113c) to said at least one actuator (115a, 115b, 115c),

temporarily connecting together said nozzle plate (112) and said substrate (111), and

joining, by means of the so-called “

anodic bonding”

technology, the assembly formed by the nozzle plate and the substrate,

whereby a structural cohesion is obtained between the two surfaces of silicon and of borosilicate glass (98), in reciprocal contact, respectively of said nozzle plate (112) and of said substrate (111).

8. Method for manufacturing an ink jet printhead (110) according to claim 7,

wherein the phrase of producing a nozzle plate (112) comprises the following steps:

providing a silicon wafer (151) comprising a plurality of elementary areas (112a, 112b, 112b) each corresponding to a nozzle plate;

forming by etching, on each of said areas, at least one chamber (120a;

112b;

112c) and one inlet duct (122) of the hydraulic circuit (121) of the corresponding nozzle plate (112), said inlet duct (122) being provided for feeding the ink (140) to said chamber (120a;

120b;

120c); and

dividing said silicon wafer into elementary units each constituting a nozzle plate (112).

9. Method for manufacturing an ink jet printhead (110) according to claim 8, wherein said silicon wafer is of the thin type and has an indicative thickness of 75 μ

m.

10. Method for manufacturing an ink jet printhead (110) according to claim 8, further comprising the following steps:

providing a silicon wafer (170) comprising a plurality of elementary areas (111a, 111b, 111c) each corresponding to a substrate (111);

providing, on said silicon wafer (170), a protection layer of conductive material consisting of a plurality of reciprocally interconnected portions in such a way as to form an equipotential mesh or network (177), wherein each portion of said conductive layer is deposited on a respective elementary area (111a, 111b, 111c) of said silicon wafer (170), and extends both along the area of said actuator (115a, 115b, 115c) for the purpose of protecting it, and along the zone of the junction (125) which will subsequently be made between the substrate (111) and the nozzle plate (112), and in addition also externally to the junction zone (125);

providing a plurality of nozzle plates (112), made separately with respect to said substrate (111),

aligning and arranging, on said silicon wafer (170), each of said nozzle plates (112) into contact with a corresponding elementary area of said silicon wafer (170);

connecting said equipotential network to a counter-electrode of an appropriate anodic bonding machine;

applying, by means of said counter-electrode, a suitable potential between said equipotential network and each nozzle plate (112) to produce said junction (125), based on the anodic bonding technology, between each elementary area (111a, 111b, 111c) of said silicon wafer (170), and corresponding nozzle plate (112), and

dividing said silicon wafer (170) into a plurality of units, each formed by a single substrate and a single nozzle plate, and constituting an ink jet printhead.

11. Method for manufacturing an ink jet printhead (110) according to claim 10, comprising, after said step of providing a plurality of nozzle plates (112) on said silicon wafer (170), a step of connecting temporarily with on adhesive each of said nozzle plates (112) to the corresponding elementary areas (111a, 11b, 111c) of said silicon wafer (170).