Technical Field
The present disclosure relates to a fluid ejection device with restriction channel and to a method for manufacturing the fluid ejection device.
Description of the Related Art
Multiple types of fluid ejection devices are known, in particular inkjet heads for printing applications. Similar heads, with appropriate modifications, may further be used for ejection of fluid other than ink, for example, for applications in the biological or biomedical field, for local application of biological material (e.g., DNA) during manufacturing of sensors for biological analyses.
Manufacturing methods envisage coupling via gluing or bonding of a large number of pre-processed wafers. This method is costly and typically requires high precision. Misalignment between the wafers during assembly may entail both structural weakness and non-optimal operation of the finished device.
One or more embodiments of the present disclosure provide a fluid ejection device with restriction channel and a method for manufacturing the fluid ejection device.
In particular, a fluid ejection device according to one embodiment includes a first semiconductor body including an actuator, a chamber for containing a fluid, and an inlet channel. The actuator is configured to cause ejection of the fluid during an operating condition of the ejection device. The inlet channel is configured to provide fluid to the chamber. The inlet channel extends in a first direction and has a section having a first dimension. The fluid ejection device also includes a second semiconductor body coupled to the first semiconductor body. The second semiconductor body has an ejection nozzle that is in fluidic communication with the chamber and is configured to expel an amount of fluid towards an environment external to the ejection device. The second semiconductor body comprises a first restriction channel fluidically coupled to the inlet channel. The first restriction channel extends in a second direction that is orthogonal to the first direction. The first restriction channel has a section having a second dimension that is smaller than the first dimension. The restriction channel forms a fluidic path that fluidically couples the inlet channel to the chamber.
For a better understanding of the present disclosure, preferred embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:
Fluid ejection devices based upon the piezoelectric technology may be manufactured by bonding or gluing together a plurality of wafers or chips previously processed employing micromachining technologies typically used for producing MEMS (Micro-Electro-Mechanical Systems) devices. In particular,
In a way not shown in detail in
An intermediate channel 11a for inlet of the fluid 6 into the chamber 10 and an intermediate channel 11b for outlet of the fluid 6 from the chamber 10 extend throughout the thickness of the wafer 2.
In use, when the piezoelectric actuator 3 is driven, a drop of the fluid 6 is expelled through one or more nozzles 13, which is provided in a further wafer or chip that is distinct from the first wafer 2. The intermediate inlet and outlet channels 11a, 11b both have a circular or polygonal shape, with a diameter d1 (measured in the direction X) between 20 μm and 200 μm, for example 100 μm, and a section area with a dimension A1 between 20 μm and 200 μm, for example 80 μm. According to one embodiment, the section of the intermediate inlet and outlet channels 11a, 11b is uniform throughout their extension along Z.
A second chip or wafer 4, which lies in a plane parallel to the plane XY and is arranged on the first wafer 2, has one or more chambers 5 for containing the piezoelectric actuators 3 such as to isolate, in use, the piezoelectric actuators 3 from the fluid 6 to be expelled and from the environment. The second wafer 4 further has a channel 9a for inlet of the fluid 6 and a channel 9b for outlet of the fluid 6 not ejected through the nozzle 13, thus enabling recirculation of the fluid 6. The inlet and outlet channels 9a, 9b are through holes made through the second wafer 4. The inlet and outlet channels 9a, 9b both have a circular or polygonal shape, with diameter d2 (measured in the direction X) greater than the diameter d1, and between 30 μm and 1000 μm, for example 180 μm. The inlet channel 9a may be coupled to a reservoir for supplying fluid to the chamber 10. The inlet and outlet channels 9a, 9b further have a section area with a dimension A2 between 50 μm and 1000 μm, for example 200 μm, where A2 is chosen greater than A1. According to one embodiment, the section of the inlet and outlet channels 9a, 9b is uniform throughout their extension along Z.
The inlet channel 9a is fluidically coupled to the intermediate inlet channel 11a, and the outlet channel 9b is fluidically coupled to the intermediate outlet channel 11b. In greater detail, the inlet and outlet channels 11a, 11b are respectively aligned, in a direction Z orthogonal to the plane XY, to the inlet and outlet channels 9a, 9b.
A third chip or wafer 8, which lies in a plane parallel to the plane XY and is arranged underneath the first wafer 2, has the nozzle 13 for ejection of the fluid 6 in fluidic connection with the chamber 10.
Coupling of the first and third wafers 2, 8 enables formation of the chamber 10, the latter being delimited in part by the first wafer 2 and in part by the third wafer 8.
According to an aspect of the present disclosure, the third wafer 8 has a first restriction channel 16 and a second restriction channel 18, each in the form of a trench that extends in depth in the direction Z and longitudinally in the plane XY, with main extension along X. The first and second restriction channels 16, 18 fluidically connect, respectively, the intermediate inlet channel 11a with the chamber 10 and the chamber 10 with the intermediate outlet channel 11b. More in particular, according to an aspect of the present disclosure, the first and second restriction channels 16, 18 are fluidically connected directly to the chamber 10. The first and second restriction channels 16, 18 have: a depth d3, along Z, between 2 μm and 300 μm, for example, 30 μm; a main extension d4, along X, between 2 μm and 300 μm, for example, 40 μm; and a secondary extension (not represented), along Y, between 10 μm and 1000 μm, for example, 400 μm.
More in particular, the first and second restriction channels 16, 18 have a uniform section (area) transverse to the direction of flow of the fluid (in this case, X) having a dimension A3 between 2 μm and 300 μm, for example, 30 μm. According to a different embodiment, the first restriction channel 16 has a section that is not uniform, but such as to have a maximum value of dimension at the intersection between the first restriction channel 16 and the intermediate inlet channel 11a in order to facilitate (during manufacturing) coupling together, as well as entry of the fluid coming from the intermediate inlet channel 11a into the first restriction channel 16. Alternatively, or in addition, also the second restriction channel 18 has a maximum value of dimension of section at the intersection thereof with the intermediate outlet channel 11b in order to facilitate (during manufacture) the step of coupling thereof.
Irrespective of the embodiment, the first and second restriction channels 16, 18 have at least a respective section smaller than any section of the intermediate inlet and outlet channels 11a, 11b, respectively.
Further, the first and second restriction channels 16, 18 have at least a respective section smaller than any section of the inlet and outlet channels 9a, 9b, respectively.
In use, the fluid 6 flows through the inlet channel 9a and the intermediate inlet channel 11a in the direction Z, and then flows through the first restriction channel 16, in the direction X, orthogonal to the direction Z, and then enters the chamber 10. In use, as a result of the deflection of the membrane 7 towards the inside of the chamber 10, controlled by the piezoelectric actuator 3, a portion of the fluid 6 is ejected through the nozzle 13, while another portion of the fluid 6 is conveyed towards the outlet channel 9b, flowing first in the direction X through the second restriction channel 18 and then in the direction Z through the intermediate outlet channel 11b and the outlet channel 9b.
The first and second restriction regions have the function of reducing the flow of the fluid 6 in a direction opposite to the one previously described (in particular, reducing return of the fluid 6 towards the inlet channel) during ejection of the fluid 6 through the nozzle 13. Provision of the first and second restriction channels 16, 18 in the third wafer 8, which have a main extension parallel to the plane of lie of the third wafer 8, makes it possible to limit the thickness, along Z, of the ejection device 1 and to facilitate coupling between the wafers 2, 4, and 8 in so far as it is not necessary to meet precise requirements or specifications of alignment between the channels. In fact, it is sufficient for the intermediate inlet channel 11a and the first restriction channel 16 to be in fluidic communication with one another for the characteristics of operation of the ejection device 1 not to be jeopardized.
According to an embodiment of the present disclosure, the aforementioned wafers 2, 4, 8 are of semiconductor material such as silicon, and may be chips or dice that were formed from respective wafers, each including a plurality of chips that are separated in a dicing process. Conductive layers of doped silicon, or doped polysilicon, or metal, may further be provided (in a per se known manner, not shown in the figure) for electrically coupling the piezoresistive element to conductive pads 21, used for driving the piezoelectric element 3 so as to cause deflection of the membrane 7. Dielectric or insulating layers may further be present, according to the need.
The wafers 2, 4, 8 are assembled together by interface bonding regions and/or gluing regions and/or adhesive regions. Said regions are not shown in detail in
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According to what has been described so far, the passivation layer 218 does not coat completely the top electrode 228, which may thus be electrically contacted by a conductive path. Instead, the bottom electrode 224 is not electrically accessible, since it is completely protected by the overlying piezoelectric element 226 and the passivation layer 218. Simultaneously, a step of selective removal of a portion of the passivation layer 218 is carried out in an area corresponding to the bottom electrode 224, and in particular to the portion of the bottom electrode 224 that extends, in the plane XY, beyond the outer edge of the piezoelectric element 226. In this way, a region 224′ of the bottom electrode 224 is exposed and may thus be electrically contacted by an own conductive path. The openings for forming the electrical contacts with the top electrode 228 and the bottom electrode 224 may be formed during a same lithographic and etching step (in particular using a same mask).
The step of formation of a first conductive path 221 and a second conductive path 223 is shown in
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As an alternative to what has been described, it is further possible to etch the substrate 201 on surface portions exposed through the trenches 225a, 225b, to form the through holes 233a, 233b. In this way, it is not necessary to provide alignment markers.
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A further step of masked etching (
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With reference to the wafer 4, the portions of the structural layer 409 that extend to a height, along Z, greater than does the recess that forms the chamber 5, are the regions provided for mechanical coupling with the wafer 2. During the coupling step shown in
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Formed on the first surface 801a, for example by thermal oxidation, is an interface layer 803, of silicon oxide (SiO2). The interface layer 803 has, for instance, a thickness between approximately 0.5 μm and 5 μm, in particular approximately 1 μm.
On the interface layer 803 a structural layer 805 of epitaxially grown polysilicon is formed, having a thickness between approximately 10 and 1000 μm, in particular approximately 25 μm. In particular, the structural layer 805 is grown epitaxially until it reaches a thickness greater than the desired thickness (for example, approximately 3 μm ticker), and is then subjected to a CMP (Chemical Mechanical Polishing) step to reduce the thickness thereof and obtain a top surface 805a with low roughness.
The structural layer 805 may be of a material other than polysilicon, for example silicon or some other material, provided that it may be removed in a way selective in regard to the material of which the interface layer 803 is made.
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To facilitate execution of subsequent manufacturing steps, the second wafer 4 may be coupled, by a thermal-release biadhesive tape, with a further wafer, having the sole function of favoring handling of the device that is being produced. This step is not shown in the figures. At the end of the manufacturing process, said further handling wafer will be removed. The handling wafer is, for example, of silicon and has a thickness of approximately 500 μm. The thermal-release biadhesive tape is, for example, laid on said wafer by lamination.
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It is thus advisable, in this step, to provide alignment markers (not shown) on the exposed interface layer 803. Said markers have the function of identifying with high precision, in subsequent processing steps, the spatial arrangement of the hole 808, to complete formation of the fluid ejection nozzle.
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Finally, the resist mask 810 is then removed, thus completing formation of the nozzle 13. The device 1 of
From an examination of the characteristics of the disclosure provided according to the present disclosure, the advantages that it affords are evident.
In particular, the steps for manufacturing the liquid-ejection device according to the present disclosure specifies coupling of just three wafers, thus reducing the risks of misalignment, in so far as just two steps of coupling of wafers are utilized, and limiting the manufacturing costs.
Further, the risks of misalignment are further reduced by providing the restriction channels 16, 18 with a main extension in the plane of lie of the third wafer 8, i.e., in a direction orthogonal both to the direction of supply of the fluid from the inlet hole 9a and to the direction of ejection from the nozzle 13. Due to this, no special arrangements are necessary for coaxial coupling of channels that have sections different from one another, as is, instead, the case in the prior art where the restriction channels 16, 18 have a main extension coinciding with the direction of supply of the fluid from the inlet hole.
Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the scope of the present disclosure.
In particular, the embodiment described and shown in the figures comprises a single nozzle. Practical applications generally specify formation of a plurality of nozzles according to the amount of liquid to be ejected. In this case, the ejection device will be formed by a plurality of base ejection modules of the type described and represented in the figures, adjacent to one another and obtained with common micromachining steps starting from the same wafers of semiconductor material.
The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
Number | Date | Country | Kind |
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102015000078380 | Nov 2015 | IT | national |