Patent Description:
In some fluid ejection devices, fluid droplets are ejected from one or more nozzles onto a medium. The nozzles are fluidically connected to a fluid path that includes a fluid pumping chamber. The fluid pumping chamber can be actuated by an actuator, which causes ejection of a fluid droplet. The medium can be moved relative to the fluid ejection device. The ejection of a fluid droplet from a particular nozzle is timed with the movement of the medium to place a fluid droplet at a desired location on the medium. Ejecting fluid droplets of uniform size and speed and in the same direction enables uniform deposition of fluid droplets onto the medium.

<CIT> describes an apparatus for ejecting ink droplets where ink is filtered by a filter feature and subsequently in part discharged from a nozzle and in part returned to an ink tank via a discharge path and a circulation tube.

When fluid is ejected from a nozzle of a fluid ejector, the nozzle can become at least partially depleted of fluid, rendering the nozzle unprepared for ejection of further droplets. Circulation of fluid through "leakage" flow paths to the nozzle can refill the depleted nozzle. If these leakage flow paths have a large cross-sectional area, the depleted nozzle can be refilled quickly after fluid is ejected from the nozzle, the nozzle can be readied more quickly for subsequent fluid ejections. However, large leakage flow paths can make it difficult to achieve a high enough pressure at the nozzle opening for efficient fluid ejection. In order to achieve both rapid nozzle refilling and sufficiently high nozzle pressure, an impedance feature can be positioned in the flow path. The impedance feature introduces a fluidic impedance into the leakage flow path that is higher at or around the jet resonance frequency than at other frequencies. The jet resonance frequency is the frequency at which the nozzle has high fluid flow, such as during fluid ejection from the nozzle. As a result of the higher fluidic impedance introduced by the impedance feature at the jet resonance frequency, the fluidic impedance in the flow paths is higher during fluid ejection than at other times, e.g., during refilling, thus enabling sufficiently high pressures to be achieved during ejection and while still providing rapid refilling of the depleted nozzle when no fluid is being ejected. The impedance feature can be a membrane with apertures positioned in the fluid supply or return path.

Another issue is that fluid can contain contaminants, e.g., impurities, that can clog or damage a nozzle. It is useful to have a filter to prevent such contaminants from reaching the nozzle or from being ejected onto the surface. The impedance feature can be a membrane with apertures positioned in the fluid supply path.

In a first aspect, a fluid ejector includes a nozzle layer, a body, an actuator, a first membrane, and a second membrane. The nozzle layer has an outer surface, an inner surface, and a nozzle extending between the inner surface and the outer surface. The nozzle has an entrance at the inner surface to receive fluid and an exit opening at an outer surface for ejection of fluid. The inner surface of the nozzle layer is secured to the body. The body includes a pumping chamber, a return channel, and a first passage fluidically connecting the pumping chamber to the entrance of the nozzle. A second passage fluidically connects the entrance of the nozzle to the return channel. The actuator is configured to cause fluid to flow out of the pumping chamber such that actuation of the actuator causes fluid to be ejected from the nozzle. The first membrane is disposed between the actuator and the pumping chamber and isolating the actuator from fluid in the pumping chamber. The second membrane is different from the first membrane, and the second membrane is formed across and partially blocks the entrance of the nozzle. The second membrane has at least one hole therethrough such that in operation of the fluid ejector fluid flows through the at least one hole in the second membrane.

Implementations may include one or more of the following features.

The second membrane and hole may be configured such that the first flow path has a first impedance when fluid is being ejected from the nozzle and a second impedance when fluid is not being ejected from the nozzle. The first impedance may be greater than the second impedance. The second membrane may be configured such that second passage has a maximum impedance at or around a resonance frequency of the nozzle.

The second membrane may extend substantially parallel to the outer surface.

The second membrane may have a plurality of holes therethrough. The plurality of holes may be spaced uniformly across the second membrane. The plurality of holes may be configured to provide a filter.

The second membrane may extend substantially parallel to the outer surface. The second membrane may project inwardly substantially perpendicular to walls of the nozzle. The second membrane may be formed of a material that has a lower elastic modulus than an elastic modulus of a material forming walls of the nozzle. The second membrane may be more flexible than walls of the nozzle. The hole through the second membrane may be narrower than the exit opening of the nozzle.

The second membrane may be formed of an oxide, and may have a thickness between about <NUM> and about <NUM>. The second membrane may be formed of a polymer, and may have a thickness between about <NUM> and about <NUM>.

In another aspect, a method of fluid ejection includes ejecting fluid from a nozzle of a fluid ejector as described above, and refilling the nozzle with fluid from a flow path. The second membrane is formed across the flow path and provides the flow path with a first impedance when fluid is being ejected from the nozzle and a second impedance when fluid is not being ejected from the nozzle. The second membrane has at least one hole therethrough.

Refilling the nozzle may include flowing fluid in the flow path through the at least one hole defined by the second membrane. The flow path may fluidically connect the nozzle to a return channel. The flow path may fluidically connect the nozzle to a pumping chamber. Ejecting fluid from the nozzle may include actuating an actuator to cause fluid to be ejected from a pumping chamber fluidically connected to the nozzle.

The approaches described here can have one or more of the following advantages.

The impedance feature allow sufficiently high pressures to be achieved during fluid ejection while also allowing rapid refilling of depleted nozzles. The impedance feature can be fabricated using existing fabrication techniques and with few additional steps, and thus can be easily integrated into current process flows.

A filter feature can prevent impurities in from reaching and clogging the nozzle or from being ejected onto the surface. The filter can be fabricated in conjunction with compliance features in a supply or return channel without significantly increasing fabrication complexity.

Referring to <FIG>, a printhead <NUM> can be used for ejecting droplets of fluid, such as ink, biological liquids, polymers, liquids for forming electronic components, or other types of liquid, onto a surface. The printhead <NUM> can include a casing <NUM> that provides a chamber for holding fluid, a substrate <NUM> with nozzles and actuators for ejecting fluid from the nozzles, and an interposer <NUM> to carry fluid from the chamber to the substrate <NUM>. Although one implementation of the casing and interposer for the printhead is described below, other configurations are possible for the printhead, and the casing and interposer are, in fact, optional. For example, flexible tubing could connect inlets and outlets on a top surface of the substrate <NUM> to a fluid reservoir.

The casing <NUM> has an interior volume that is divided into a fluid supply chamber <NUM> and a fluid return chamber <NUM>, e.g., by divider wall <NUM>.

The bottom of the fluid supply chamber <NUM> and the fluid return chamber <NUM> can be defined by the top surface of the interposer assembly <NUM>. The interposer assembly <NUM> can be attached to the casing <NUM>, e.g., onto the bottom surface of the casing <NUM>, such as by bonding, friction, or another mechanism of attachment. The interposer assembly can include an upper interposer <NUM> and a lower interposer <NUM> positioned between the upper interposer <NUM> and a substrate <NUM>. In some implementations, the interposer assembly consists of a single interposer body.

Passages formed in the interposer assembly <NUM> and the substrate <NUM> define a flow path <NUM> for fluid flow. The interposer assembly <NUM> includes a fluid supply inlet opening <NUM> and a fluid return outlet opening <NUM>. For instance, the fluid supply inlet opening <NUM> and fluid return outlet opening <NUM> can be formed as apertures in the upper interposer <NUM>. Fluid can flow along the flow path <NUM> from the supply chamber <NUM>, through the fluid supply inlet <NUM> to one or more fluid ejectors <NUM> (described in greater detail below) in the substrate <NUM>. An actuator <NUM> in the fluid ejector <NUM> can cause a portion of the fluid to be ejected through a nozzle <NUM>. The remaining fluid that is not ejected can flow along the flow path <NUM> from one or more fluid ejection devices <NUM> in the substrate <NUM> through the fluid return outlet opening <NUM> and into the return chamber <NUM>.

In <FIG>, a single flow path <NUM> is shown as a straight passage for illustrative purposes. However, the printhead <NUM> can include multiple flow paths <NUM>, and the flow paths <NUM> can be considerably more geometrically complex, e.g., the flow paths are not necessarily straight.

Referring to <FIG> and <FIG>, the substrate <NUM> can include a body <NUM> in which various passages of the fluid path, such as the pumping chamber are formed, a nozzle layer <NUM> in which the nozzles <NUM> are formed, and the actuators <NUM> for the fluid ejectors <NUM>. The substrate <NUM> can be formed by semiconductor chip fabrication processes.

Passages through the substrate <NUM> define a flow path <NUM> for fluid through the substrate <NUM>. In particular, a substrate inlet <NUM> receives fluid, e.g., from the supply chamber <NUM> via the fluid supply inlet <NUM> in the interposer assembly. The substrate inlet <NUM> extends through a membrane layer <NUM> (discussed in more detail below), and supplies fluid to one or more inlet feed channels <NUM>. The inlet feed channels <NUM> are also called supply channels. Each inlet feed channel <NUM> supplies fluid to multiple fluid ejectors <NUM> through a corresponding inlet passage (not shown). Fluid can be selectively ejected from the nozzle <NUM> of each fluid ejector <NUM> to print onto a surface. For simplicity, only one fluid ejector <NUM> is shown in <FIG> and <FIG>. The possible location of descenders of other fluid ejectors are shown in phantom in <FIG>.

The body <NUM> can be a monolithic body, e.g., a monolithic semiconductor body, such as a silicon substrate. For example, the body <NUM> can be single-crystal silicon.

Each fluid ejector includes a nozzle <NUM> formed in a nozzle layer <NUM> that is disposed on a bottom surface of the substrate <NUM>. In some implementations, the nozzle layer <NUM> is an integral part of the substrate <NUM>, e.g., the nozzle layer <NUM> is formed of the same material and crystalline structure, e.g., single crystal silicon, as the body <NUM>. In some implementations, the nozzle layer <NUM> is a layer of different material, e.g., silicon oxide, that is deposited onto the surface of the body <NUM> to form the substrate <NUM>. In some implementations, the nozzle layer <NUM> comprises multiple layers, e.g., a silicon layer and one or more oxide layers.

Fluid flows through each fluid ejector <NUM> along an ejector flow path <NUM>. The ejector flow path <NUM> can include a pumping chamber inlet passage <NUM>, a pumping chamber <NUM>, a descender <NUM>, and an outlet passage <NUM>. The pumping chamber inlet passage <NUM> fluidically connects the pumping chamber <NUM> to the inlet feed channel <NUM> and can include, e.g., an ascender that extends vertically from the inlet feed channel <NUM> a pumping chamber inlet that extends horizontally from the ascender to the pumping chamber. The descender <NUM> is fluidically connected to a corresponding nozzle <NUM>, e.g., at the bottom of the descender. The outlet passage <NUM> connects the descender <NUM> to an outlet feed channel <NUM>, which is in fluidic connection with the return chamber through a substrate outlet and the fluid supply outlet <NUM> (see <FIG>). The outlet feed channel <NUM> is also called a return channel.

The descender <NUM> is fluidically connected to a corresponding nozzle <NUM>, e.g., at the bottom of the descender <NUM>. In general, the nozzle <NUM> can be considered the portion of the flow path after the intersection of the outlet passage <NUM> to the descender.

In the example of <FIG> and <FIG>, passages such as the substrate inlet <NUM>, the inlet feed channel <NUM>, and the outlet feed channel <NUM> are shown in a common plane. However, in some implementations (e.g., in the examples of <FIG> and <FIG>), one or more of the substrate inlet <NUM>, the inlet feed channel <NUM>, and the outlet feed channel <NUM> are not in a common plane with the other passages.

Referring to <FIG> and <FIG>, the substrate <NUM> includes multiple inlet feed channels <NUM> formed therein and extending parallel with one another and to the plane of the bottom surface <NUM> (see <FIG>) of the substrate <NUM>. Each inlet feed channel <NUM> is in fluidic communication with at least one substrate inlet <NUM> that extends perpendicular to the inlet feed channels <NUM>, e.g., perpendicular to the plane of the bottom surface <NUM> of the substrate <NUM>. The substrate <NUM> also includes multiple outlet feed channels <NUM> formed therein and extending parallel with one another and to the plane of the bottom surface <NUM> of the substrate <NUM>. Each outlet feed channel <NUM> is in fluidic communication with at least one substrate outlet (not shown) that extends perpendicular to the outlet feed channels <NUM>, e.g., perpendicular to the plane of the bottom surface <NUM> of the substrate <NUM>. In some examples, the inlet feed channels <NUM> and the outlet feed channels <NUM> are arranged in alternating rows.

The outlet feed channel <NUM> has a larger cross-sectional area than an outlet passages <NUM>, e.g., to handle the combined multiple outlet feed channels <NUM>. For example, as shown in <FIG>, the outlet feed channel <NUM> can have a height (measured perpendicular to the surface 11a) that is larger than the height of the outlet passages <NUM>. Similarly, as shown in <FIG>, the outlet feed channel <NUM> can have a width (measured parallel to the surface 11a) that is larger than the width of the outlet passages <NUM>.

Returning to <FIG> and <FIG>, the substrate includes multiple fluid ejectors <NUM>. Fluid flows through each fluid ejector <NUM> along a corresponding ejector flow path <NUM>, which includes the pumping chamber inlet passage <NUM> (including an ascender 16a and a horizontal pumping chamber inlet 16b), a pumping chamber <NUM>, and a descender <NUM>. Each ascender 16a is fluidically connected to one of the inlet feed channels <NUM>. Each ascender 16a is also fluidically connected to the corresponding pumping chamber <NUM> through the pumping chamber inlet 16b. The pumping chamber <NUM> is fluidically connected to the corresponding descender <NUM>, which leads to the associated nozzle <NUM>. Each descender <NUM> is also connected to one of the outlet feed channels <NUM> through the corresponding outlet passage <NUM>. For instance, the cross-sectional view of fluid ejectors of <FIG> can be taken along line <NUM>-<NUM> of <FIG>.

In some examples, the printhead <NUM> includes multiple nozzles <NUM> arranged in parallel columns <NUM> (see <FIG>). The nozzles <NUM> in a given column <NUM> can be all fluidically connected to the same inlet feed channel <NUM> and the same outlet feed channel <NUM>. That is, for instance, all of the ascenders <NUM> in a given column can be connected to the same inlet feed channel <NUM> and all of the descenders <NUM> in a given column can be connected to the same outlet feed channel <NUM>.

In some implementations, nozzles <NUM> in adjacent columns can all be fluidically connected to the same inlet feed channel <NUM> or the same outlet feed channel <NUM>, but not both. For instance, in the example of <FIG>, each nozzle <NUM> in column 23a is fluidically connected to the inlet feed channel 14a and to the outlet feed channel 28a. Each nozzle <NUM> in the adjacent column 23b is also connected to the inlet feed channel 14a but is connected to the outlet feed channel 28b.

In some implementations, columns of nozzles <NUM> can be connected to the same inlet feed channel <NUM> or the same outlet feed channel <NUM> in an alternating pattern. In some implementations, columns of nozzles <NUM> can be connected to the same inlet feed channel <NUM> or the same outlet feed channel <NUM> in an alternating pattern. In some implementations, the walls 14a of the inlet feed channels <NUM> have indentations, e.g., form a scalloped, wavy or zigzag pattern, to disrupt cross-talk. Further details about the printhead <NUM> can be found in <CIT>.

Referring again to <FIG>, each fluid ejector <NUM> includes a corresponding actuator <NUM>, such as a piezoelectric transducer or a resistive heater. The pumping chamber <NUM> of each fluid ejector <NUM> is in close proximity to the corresponding actuator <NUM>. Each actuator <NUM> can be selectively actuated to pressurize the corresponding pumping chamber <NUM>, thus ejecting fluid from the nozzle <NUM> that is connected to the pressurized pumping chamber.

In some examples, the actuator <NUM> can include a piezoelectric layer <NUM>, such as a layer of lead zirconium titanate (PZT). The piezoelectric layer <NUM> can have a thickness of about <NUM> or less, e.g., about <NUM> to about <NUM>, e.g., about <NUM> to about <NUM>. In the example of <FIG>, the piezoelectric layer <NUM> is continuous. In some examples, the piezoelectric layer <NUM> can be made discontinuous, e.g., by an etching or sawing step during fabrication. The discontinuous piezoelectric layer <NUM> can overlie at least the pumping chamber <NUM>, but not the entire body <NUM>.

The piezoelectric layer <NUM> is sandwiched between a drive electrode <NUM> and a ground electrode <NUM>. The drive electrode <NUM> and the ground electrode <NUM> can be metal, such as copper, gold, tungsten, titanium, platinum, or a combination of metals, or another conductive material, such as indium-tin-oxide (ITO). The thickness of the drive electrode <NUM> and the ground electrode <NUM> can be, e.g., about <NUM> or less, e.g., about <NUM>.

A membrane <NUM> is disposed between the actuator <NUM> and the pumping chamber <NUM> and isolates the actuator <NUM>, e.g., the ground electrode <NUM>, from fluid in the pumping chamber <NUM>. In some implementations, the membrane <NUM> is a separate layer, e.g., a layer of silicon oxide, from the body <NUM>. In some implementations, the membrane is unitary with the body <NUM>, e.g., the nozzle layer <NUM> is formed of the same material and crystalline structure, e.g., single crystal silicon, as the body <NUM>. In some implementations, two or more of the substrate <NUM>, the nozzle layer <NUM>, and the membrane <NUM> can be formed as a unitary body. In some implementations, the actuator <NUM> does not include a membrane <NUM>, and the ground electrode <NUM> is formed on the back side of the piezoelectric layer <NUM> such that the ground electrode <NUM> is directly exposed to fluid in the pumping chamber <NUM>.

To actuate the piezoelectric actuator <NUM>, an electrical voltage can be applied between the drive electrode <NUM> and the ground electrode <NUM> to apply a voltage to the piezoelectric layer <NUM>. The applied voltage causes the piezoelectric layer <NUM> to deflect, which in turn causes the membrane <NUM> to deflect. The deflection of the membrane <NUM> causes a change in volume of the pumping chamber <NUM>, producing a pressure pulse (also referred to as a firing pulse) in the pumping chamber <NUM>. The pressure pulse propagates through the descender <NUM> to the corresponding nozzle <NUM>, thus causing a droplet of fluid to be ejected from the nozzle <NUM>.

The membrane <NUM> can be a single layer of silicon (e.g., single crystalline silicon), another semiconductor material, one or more layers of oxide, such as aluminum oxide (AlO2), zirconium oxide (ZrO2), or silicon oxide (SiO<NUM>), aluminum nitride, silicon carbide, ceramics or metal, or another material. For instance, the membrane <NUM> can be formed of an inert material that has a compliance such that the actuation of the actuator <NUM> causes flexure of the membrane <NUM> sufficient to cause a droplet of fluid to be ejected.

In some implementations, the membrane <NUM> can be secured to the actuator <NUM> with an adhesive layer <NUM>. In some implementations, the layers of the actuator <NUM> are deposited directly on the membrane <NUM>.

When fluid is ejected from the nozzle <NUM> of a fluid ejector <NUM>, the nozzle <NUM> can become at least partially depleted of fluid. Circulation of fluid through the inlet and outlet feed channels <NUM>, <NUM> (sometimes referred to generally as feed channels) can provide fluid to refill the depleted nozzle <NUM>. Without being limited to any particular theory, although fluid can flow through the outlet passage <NUM> toward the toward the outlet feed channel <NUM> during ejection of a droplet of fluid, after ejection when the nozzle <NUM> is depleted, it is also possible for fluid to flow back through the outlet passage <NUM> toward the nozzle <NUM> to refill the nozzle <NUM>.

If the depleted nozzle <NUM> can be refilled quickly after ejection, the nozzle can be readied more quickly for a subsequent ejection, thus improving the response time of the fluid ejector <NUM>. For instance, the speed with which the nozzle <NUM> can be refilled can be increased by increasing the cross-sectional area of one or more of the fluid flow passages that supply fluid to the nozzle <NUM>, such as the descender <NUM>, the outlet passage <NUM>, or another fluid flow passage. However, with large fluid flow passages supplying fluid to the nozzle <NUM>, it can sometimes be difficult to achieve a high enough pressure at the nozzle opening <NUM> for efficient fluid ejection (sometimes referred to as jetting). Conversely, smaller fluid flow passages supplying fluid to the nozzle <NUM> can make it easier to achieve pressures sufficient for efficient jetting, but can also limit the speed with which the nozzle <NUM> can be refilled.

Referring to <FIG> and <FIG>, in some cases, in order to achieve both rapid nozzle refilling and sufficiently high nozzle pressures during jetting, an impedance structure <NUM>, such as a membrane <NUM>, can be positioned in the fluid flow path close to the nozzle. The membrane <NUM> can have one or more holes <NUM> through the thickness of the membrane. The membrane <NUM> is positioned in the flow path such that fluid flows through the holes <NUM> in the membrane <NUM>.

In the example of <FIG>, the membrane <NUM> is positioned in the outlet passage <NUM> and provides the impedance structure <NUM>. In this example, the outlet passage <NUM> includes a portion 32a above the membrane <NUM>, and a portion 32b below the membrane <NUM>. In the example of <FIG>, the impedance structure <NUM> includes a membrane <NUM> positioned between the outlet passage <NUM> and the return channel <NUM>. In this case, the membrane can form a bottom surface of the return channel <NUM>, e.g., the top surface of the membrane <NUM> can coplanar with the bottom surface of the return channel <NUM>.

However, the membrane <NUM> can alternatively be positioned at other locations in the inlet flow path, the outlet flow path, or both, and can provide other functions.

Referring to <FIG> and <FIG>, in some cases a filter feature <NUM> can be positioned in the fluid flow path close to the nozzle to prevent contaminants from reaching the nozzle or from being ejected from the nozzle. The filter feature <NUM> can be provided by a membrane <NUM> having one or more holes <NUM> through the thickness of the membrane.

As shown in <FIG>, the membrane <NUM> can be positioned across the nozzle <NUM> after (i.e., closer to the nozzle opening <NUM> than) the intersection between the descender <NUM> and the outlet passage <NUM>. For example, the membrane <NUM> can be positioned immediately after the intersection, e.g., the top surface of the membrane can be co-planar with the bottom surface of the outlet passage <NUM>. As shown in <FIG>, the membrane <NUM> can be positioned across the descender <NUM> before (i.e., farther from the nozzle opening <NUM> than) the intersection between the descender <NUM> and the outlet passage <NUM>. For example, the membrane can be positioned immediately before the intersection, e.g., the bottom surface of the membrane can be co-planar with the top surface of the outlet passage <NUM>.

In each of the above examples of <FIG>, the membrane <NUM> lies in a plane parallel to the outer surface 11a of the nozzle layer <NUM>. Thus the holes can extend perpendicular to the outer surface 11a of the nozzle layer <NUM>.

Turning to <FIG> and <FIG>, as the impedance structure <NUM>, the membrane <NUM> can be configured to introduce a fluidic impedance to the flow passage in which the impedance membrane is positioned, such as the fluid flow path between the descender and the return channel. The value of the fluidic impedance introduced by the impedance membrane <NUM> can be dependent on frequency. For instance, oscillations can occur in the fluid in the flow passage. The impedance membrane can introduce a fluidic impedance at or around a particular frequency of the fluid oscillations that is higher than the fluidic impedance at other frequencies of the fluid oscillations. For instance, the impedance membrane <NUM> can provide a high impedance at or around the jet resonance frequency, which is the frequency at which the nozzle <NUM> has high fluid flow during jetting. In some implementations of the fluid ejector <NUM>, the jet resonance frequency is between about <NUM> and <NUM>. In some implementations, the impedance is about 20dB or a factor of <NUM>.

At or around the jet resonance frequency (e.g., when the nozzle <NUM> is ejecting fluid), the impedance membrane <NUM> thus introduces a sufficiently high fluidic impedance into the fluid flow passage in the vicinity of the nozzle <NUM> to direct fluid flow and pressure to the nozzle to provide efficient jetting. At other frequencies (e.g., frequencies not at or around the jet resonance frequency, such as when the nozzle <NUM> is not ejecting fluid), the impedance membrane introduces a lower fluidic impedance, thus enabling rapid refilling of the depleted nozzle.

In order to achieve a higher fluidic impedance at certain frequencies (e.g., at or around the jet resonance frequency) and a lower fluidic impedance at other frequencies, the impedance membrane <NUM> can act as a capacitor that is in parallel with an inductor along the fluid flow path. For instance, the membrane <NUM> itself can be a compliant membrane that acts as a capacitive element in the fluid flow path, and the holes <NUM> act as the inductor element. In this case, when a volume on one side of the membrane is pressurized, the membrane will move and hence there will be some viscous resistance. However, without being limited to any particular theory, impedance effects from the holes can dominate.

In some cases, the compliance of the membrane <NUM> can also provide a resistance that can help to dampen oscillations in the fluid flow passage, e.g., as discussed below.

As the filter feature <NUM>, the membrane <NUM> can also act as a filter to prevent foreign bodies, such as impurities in the fluid, from reaching and clogging the nozzle <NUM>. For example, the membrane <NUM> shown in <FIG> and <FIG> can act primarily as a filter rather than to adjust the fluidic impedance to affect the rate of refilling of the depleted nozzle.

The membrane <NUM> can be formed of a material that is compatible with fabrication processes (e.g., microelectromechanical systems (MEMS) fabrication processes) used to fabricate other components of the fluid ejectors <NUM>. For instance, in some cases, the membrane <NUM> can be formed of an oxide (e.g., SiO<NUM>), a nitride (e.g., Si<NUM>N<NUM>), or another insulating material. In some cases, the membrane <NUM> can be formed of silicon. In some cases, the membrane <NUM> can be formed of metal, e.g., a sputtered metal layer. In some cases, the membrane <NUM> can be formed of a relatively soft and compliant material, such as polyimide or a polymer (e.g., poly(methyl methacrylate) (PMMA), polydimethylsiloxane (PDMS), or another polymer). In some cases, the membrane <NUM> can be formed of a material that is more flexible or softer than the material forming the walls of the fluid flow path, e.g., a material that has a lower elastic modulus than the material forming the walls of the fluid flow path. In some cases, the thickness of the membrane <NUM> can cause the membrane <NUM> to be more flexible than the walls of the fluid flow path.

In general, when acting as an impedance feature, the membrane <NUM> can be thin enough to be able to deflect slightly in order to act as a capacitive element in the fluid flow path. The membrane <NUM> is also thick enough to be durable against expected pressure fluctuations or fluid flow oscillations. The appropriate thickness ti of the impedance membrane <NUM> to provide this functionality depends on properties of the membrane material, such as the elastic modulus of the membrane material.

As either a filter feature or impedance feature, a membrane <NUM> formed of SiO<NUM> can have a thickness of between about <NUM> and about <NUM>, e.g., about <NUM>, about <NUM>, or about <NUM>. A membrane <NUM> formed of a compliant polymer can have a thickness of between about <NUM> and about <NUM>, e.g., about <NUM>, about <NUM>, or about <NUM>, e.g., depending on the modulus of the polymer. The size of the membrane <NUM> is determined by the size of the flow passage in which the membrane is placed; for instance, the lateral dimensions of the membrane match the cross-sectional width and depth of the flow passage.

Characteristics of the holes <NUM> in the membrane <NUM>, such as the number, size, shape, and/or arrangement of the holes <NUM>, can be selected such that the impedance of the membrane <NUM> is highest at the desired frequency (e.g., at or around the jet resonance frequency). For instance, there can be between one and ten holes <NUM> in the impedance membrane <NUM>, e.g., <NUM> holes, <NUM> holes, <NUM> holes, <NUM> holes, or another number of holes. The holes <NUM> can have a lateral dimension (e.g., a radius r) of between about <NUM> and about <NUM>, e.g., about <NUM>, <NUM>, <NUM>, or <NUM>. The holes <NUM> can be circles, ovals, ellipses, or other shapes. For instance, the holes <NUM> can be shaped such that there are no sharp corners where mechanical stresses can be concentrated. The holes <NUM> can be arranged in ordered patterned, such as a rectangular or hexagonal array, or can be randomly distributed.

In some cases, when the actuator <NUM> of one of the fluid ejectors <NUM> is actuated, a pressure fluctuation can propagate through the ascender <NUM> of the fluid ejector <NUM> and into the inlet feed channel <NUM>. Likewise, energy from the pressure fluctuation can also propagate through the descender <NUM> of the fluid ejector <NUM> and the outlet passage <NUM> and into the outlet feed channel <NUM>. In some cases, this application refers to the inlet feed channel <NUM> and the outlet feed channel <NUM> generally as a feed channel <NUM>, <NUM>. Pressure fluctuations can thus develop in one or more of the feed channels <NUM>, <NUM>, that are connected to an actuated fluid ejector <NUM>. In some cases, these pressure fluctuations can propagate into the ejector flow paths <NUM> of other fluid ejectors <NUM> that are connected to the same feed channel <NUM>, <NUM>. These pressure fluctuations can adversely affect the drop volume and/or the drop velocity of drops ejected from those fluid ejectors <NUM>, degrading print quality. For instance, variations in drop volume can cause the amount of fluid that is ejected to vary, and variations in drop velocity can cause the location where the ejected drop is deposited onto the printing surface to vary. The inducement of pressure fluctuations in fluid ejectors is referred to as fluidic crosstalk.

Fluidic crosstalk can be reduced by providing greater compliance in the fluid ejectors to attenuate the pressure fluctuations. By increasing the compliance available in the fluid ejectors, the energy from a pressure fluctuation generated in one of the fluid ejectors can be attenuated, thus reducing the effect of the pressure fluctuation on the neighboring fluid ejectors.

Referring to <FIG>, compliance can be added to the inlet feed channel <NUM>, the outlet feed channel <NUM>, or both, by forming compliant microstructures <NUM> on one or more surfaces of the inlet feed channel <NUM> and/or the outlet feed channel <NUM>. The compliant microstructures <NUM> can be, for example, membranes that span a recess and are thus able to deflect in response to pressure variations.

For instance, in the example of <FIG>, compliant microstructures <NUM> are formed in a bottom surface <NUM> of the inlet feed channel <NUM> and a bottom surface <NUM> of the outlet feed channel. In this example, the bottom surfaces <NUM>, <NUM> are provided by the top surface of the nozzle layer <NUM>. In some examples, the compliant microstructures <NUM> can be formed in a top surface of a feed channel <NUM>, <NUM> or a side wall of a feed channel <NUM>, <NUM>. The additional compliance provided by the compliant microstructures <NUM> in a feed channel <NUM>, <NUM> attenuates the energy from a pressure fluctuation in a particular fluid ejector <NUM> that is connected to that feed channel <NUM>, <NUM>. As a result, the effect of that pressure fluctuation on other fluid ejectors <NUM> connected to that same feed channel <NUM>, <NUM> can be reduced.

Referring to <FIG>, in some embodiments, the compliant microstructures <NUM> formed in the nozzle layer <NUM> of the inlet feed channel <NUM> and/or the outlet feed channel <NUM> can be recesses <NUM> in the nozzle layer <NUM> that are covered by a thin membrane <NUM> to provide cavities <NUM>. In some implementations, the membrane <NUM> is provided by the same layer that provides the membrane <NUM>.

The membrane <NUM> is disposed over the recesses <NUM> such that an inner surface <NUM> of the nozzle layer <NUM> facing into the feed channel <NUM>, <NUM> is substantially flat. In some cases, e.g., when a vacuum is present in the cavity <NUM>, the membrane <NUM> can be slightly deflected into the cavity <NUM>.

In some cases, the recesses <NUM> can be formed in the nozzle layer <NUM>, which is also referred to as the bottom wall of the inlet or outlet feed channel <NUM>, <NUM>. In some cases, the recesses <NUM> can be formed in a top wall of the inlet or outlet feed channel, which is the wall opposite the bottom wall. In some cases, the recesses <NUM> can be formed in one or more side walls of the inlet or outlet feed channel <NUM>, <NUM>, which are the walls that intersect the top and bottom walls.

Without being limited to any particular theory, when a pressure fluctuation propagates into the feed channel <NUM>, <NUM>, the membrane <NUM> can deflect into or away from the recess <NUM>, attenuating the pressure fluctuation and mitigating fluidic crosstalk among neighboring fluid ejectors <NUM> connected to that feed channel <NUM>, <NUM>. The deflection of the membrane <NUM> is reversible such that when the fluid pressure in the feed channel <NUM>, <NUM> is reduced, the membrane <NUM> returns to its original configuration. Further details about these compliant microstructures <NUM> can be found in <CIT>.

<FIG> show an example approach to fabricating the body <NUM> and nozzle layer <NUM> of the substrate <NUM>. In this example, the substrate is fabricated to have fluid ejectors <NUM> with a membrane <NUM> in the fluid flow path before the intersection between the outlet passage <NUM> and the descender <NUM>. The membrane <NUM> can provide the filter <NUM>. In addition, the substrate can be fabricated to have compliant microstructures that include one or more cavities <NUM> formed in the nozzle layer <NUM>.

Fluid ejectors <NUM> having only the membrane <NUM> or only cavities <NUM> can be fabricated according to a similar approach. For example, to fabricate a fluid ejector without the cavities <NUM>, one can simply omit the portions of the steps associated with formation of the recess <NUM> illustrated by <FIG>.

In this example, the substrate is fabricated to have a fluid ejector <NUM> having a membrane <NUM> in the fluid flow path before the intersection between the outlet passage <NUM> and the descender. In addition, the substrate can be fabricated to have one or more cavities <NUM> formed in the nozzle layer <NUM> to provide the compliant microstructures.

Referring to <FIG> and <FIG>, a first wafer <NUM> (e.g., a silicon wafer or a silicon-on-insulator (SOI) wafer) provides a nozzle wafer. The first wafer <NUM> includes a mask layer <NUM> (e.g., an oxide or nitride mask layer, such as SiO<NUM> or Si<NUM>N<NUM>), a device layer <NUM> (e.g., a silicon device layer <NUM>), an etch stop layer <NUM> (e.g., an oxide or nitride etch stop layer), and a handle layer <NUM> (e.g., a silicon handle layer). In some examples, the first wafer <NUM> does not include the etch stop layer <NUM>. In some examples, e.g., when the first wafer <NUM> is an SOI wafer, the insulator layer of the SOI wafer <NUM> acts as the etch stop layer <NUM>.

To define the nozzle positions, the mask layer <NUM> is patterned and openings that will provide the nozzles <NUM> of the fluid ejectors <NUM> are formed through the device layer <NUM> (step <NUM>), e.g., using standard microfabrication techniques including lithography and etching. For instance, a first layer of resist can be deposited onto the unpatterned mask layer <NUM> and lithographically patterned. The mask layer <NUM> can be etched to form openings through the mask layer <NUM>. Then the device layer <NUM> can be etched using the mask layer <NUM> as the mask, e.g., with a deep reactive ion etch (DRIE), potassium hydroxide (KOH) etching, or another type of etching, to form the nozzles <NUM>. The resist can be stripped before or after etching of the device layer <NUM>.

Referring to <FIG> and <FIG>, a second wafer <NUM> (e.g., a silicon wafer or an SOI wafer) includes a mask layer <NUM> (e.g., an oxide or nitride mask layer), a device layer <NUM> (e.g., a silicon device layer <NUM>), an etch stop layer <NUM> (e.g., an oxide or nitride etch stop layer <NUM>), and a handle layer <NUM> (e.g., a silicon handle layer <NUM>). The device layer <NUM> of the second wafer <NUM> can be formed of the same material as the device layer <NUM> of the first wafer <NUM>. In some examples, e.g., when the second wafer <NUM> is an SOI wafer, the insulator layer of the SOI wafer <NUM> acts as the etch stop layer <NUM>.

To define the recesses <NUM>, the mask layer <NUM> is patterned and recesses <NUM> are formed in the device layer <NUM> of the second wafer <NUM> (step <NUM>), e.g., using standard microfabrication techniques including lithography and etching. For instance, a layer of resist can be deposited onto the unpatterned mask layer <NUM> and lithographically patterned. The mask layer <NUM> can be etched to form openings through the mask layer <NUM>. Then the device layer <NUM> can be etched using the mask layer <NUM> as the mask. Although <FIG> illustrates the recess <NUM> as extending entirely through the device layer <NUM>, this is not necessary; the recess <NUM> extend only partially through the device layer <NUM>.

Referring to <FIG> and <FIG>, the second wafer <NUM> is bonded to the first wafer <NUM> (step <NUM>), e.g., using thermal bonding or another wafer bonding technique, to form an assembly <NUM>. In particular, the second wafer <NUM> is bonded to the first wafer <NUM> such that the mask layer side of the first wafer <NUM> is in contact with the mask layer side of the second wafer <NUM>. The opening <NUM> can align with the opening that will provide the nozzle <NUM>. Thus, the mask layer <NUM> can be bonded to the mask layer <NUM>. In some implementations, the mask layer <NUM> and/or the mask layer <NUM> is removed before the second wafer <NUM> is bonded to the first wafer <NUM>.

The etch stop layer <NUM> covers the recess <NUM>. Thus, the etch stop layer <NUM> can provide the membrane <NUM> and define the cavity <NUM>. Although only one recess <NUM> is shown in <FIG>, there can be multiple recesses so as to form multiple cavities. In addition, although the cavity <NUM> shown in <FIG> is below the return channel <NUM>, similar cavities can be formed in addition or alternatively below the supply channel <NUM> by forming the recesses in the appropriate locations.

Similarly, an opening <NUM> is formed entirely through the mask layer <NUM> and the device layer <NUM>, e.g., using standard microfabrication techniques including lithography and etching, to provide a portion of the descender <NUM>.

Referring to <FIG> and <FIG>, the handle layer <NUM> of the second wafer <NUM> is removed (step <NUM>), e.g., by grinding and polishing, wet etching, plasma etching, or another removal process.

Referring to <FIG> and <FIG>, holes <NUM> are etched through the etch stop layer <NUM> to form the membrane <NUM>, e.g., for filtering structure <NUM>, that is positioned close to the nozzle <NUM> and in the flow path of fluid to the nozzle (see <FIG>) (step <NUM>).

In the approach of <FIG>, the device layer <NUM>, the mask layers <NUM>, <NUM> (if present), and the device layer <NUM> together can form the nozzle layer <NUM>. The approach of <FIG> provides a thick, robust nozzle layer <NUM> that is not thinned by the fabrication of the membrane <NUM>.

The resulting assembly <NUM> with formed recesses <NUM>, membranes <NUM>, or both can be further processed (step <NUM>) to form the fluid ejectors <NUM> of the printhead, e.g., as described below and in <CIT>.

For instance, referring to <FIG>, a top surface <NUM> of the assembly <NUM>, e.g., the exposed surface of the etch stop layer <NUM>, can be bonded to a flow path wafer <NUM> (<NUM>). For instance, the top face <NUM> of the first wafer <NUM> can be bonded to the flow path wafer <NUM> using low-temperature bonding, such as bonding with an epoxy (e.g., benzocyclobutene (BCB)) or using low-temperature plasma activated bonding.

The flow path wafer <NUM> can be fabricated before bonding to have the flow passages <NUM>, such as supply channel <NUM>, chamber inlet passage <NUM>, pumping chamber <NUM>, descender <NUM>, outlet passage <NUM> and outlet feed channel <NUM>. Other elements such as actuators (not shown) can be formed before or after the assembly <NUM> is bonded to the flow path wafer <NUM>.

Referring to <FIG>, after bonding, the handle layer <NUM> and etch stop layer <NUM> can be removed, e.g., by grinding and polishing, wet etching, plasma etching, or another removal process, to expose the nozzles <NUM>. In some implementations, the etch stop layer <NUM> is not removed, but apertures are formed through the etch stop layer <NUM> to complete the nozzles. After the actuator is formed or attached, the resulting substrate generally corresponds to the substrate <NUM> shown in <FIG>.

As shown in <FIG>, the same layer <NUM> can provide the membrane <NUM> for the compliant microstructure (if present) and the membrane <NUM>. Also as shown in <FIG>, with the outlet passage <NUM> formed as a recess in the bottom of the flow path wafer <NUM>, the top surface <NUM> of the assembly <NUM> of the first and second wafers can provide the lower surface of the outlet passage <NUM>. In addition, the top surface of the membrane <NUM> can be coplanar with the lower surface of the outlet passage <NUM>.

<FIG> show another example approach to fabricating the body <NUM> and nozzle layer <NUM> of the substrate <NUM>. In this example, the substrate is fabricated to have a fluid ejector <NUM> having a membrane <NUM> in the fluid flow path before the intersection between the outlet passage <NUM> and the descender <NUM>. The membrane <NUM> can provide the filter <NUM>.

In addition, the substrate can be fabricated to have one or more cavities <NUM> formed in the nozzle layer <NUM> to provide the compliant microstructures. A fluid ejector <NUM> having only a membranes <NUM> or only cavities <NUM> can be fabricated according to a similar approach. For example, to fabricate a fluid ejector without the cavities <NUM>, one can simply begin as shown in <FIG> but with a substrate that lacks the recess <NUM>.

Referring to <FIG> and <FIG>, a first wafer <NUM> (e.g., a silicon wafer or an SOI wafer) includes a mask layer <NUM> (e.g., an oxide or nitride mask layer), a device layer <NUM> (e.g., a silicon nozzle layer <NUM>), an etch stop layer <NUM> (e.g., an oxide or nitride etch stop layer), and a handle layer <NUM> (e.g., a silicon handle layer). The first wafer <NUM> can be termed the nozzle wafer. In some examples, the first wafer <NUM> does not include the etch stop layer <NUM>. In some examples, e.g., when the first wafer <NUM> is an SOI wafer, the insulator layer of the SOI wafer acts as the etch stop layer <NUM>.

To define the nozzle positions, the mask layer <NUM> is patterned and openings that will provide the nozzles <NUM> of the fluid ejectors <NUM> are formed through the device layer <NUM> (step <NUM>), e.g., using standard microfabrication techniques including lithography and etching. For instance, a first layer of resist can be deposited onto the unpatterned mask layer <NUM> and lithographically patterned. The mask layer <NUM> can be etched to form openings through the mask layer <NUM>. Then the device layer <NUM> can be etched using the mask layer <NUM> as the mask, e.g., with a deep reactive ion etch (DRIE), potassium hydroxide (KOH) etching, or another type of etching, to form the nozzles <NUM>. The first layer of resist can be stripped.

Optionally, recesses <NUM> that extend partially, but not entirely, through the device layer <NUM> are also formed (step <NUM>), e.g., using standard microfabrication techniques. If recesses <NUM> are to be formed, a second layer of resist can be deposited onto the mask layer <NUM> and lithographically patterned. The mask layer <NUM> and the device layer <NUM> can be etched according to the patterned resist to form the recesses <NUM>, e.g., using a wet etch or dry etch.

Referring to <FIG> and <FIG>, a second wafer <NUM> (e.g., a silicon wafer or an SOI wafer) has a handle layer <NUM>, an etch stop layer <NUM> (e.g., an oxide or nitride etch stop layer), and a device layer <NUM>. In some examples, e.g., when the second wafer <NUM> is an SOI wafer, the insulator layer of the SOI wafer <NUM> acts as the etch stop layer <NUM>.

An opening <NUM> is formed entirely through the mask layer <NUM> and the device layer <NUM>, e.g., using standard microfabrication techniques including lithography and etching, to provide a portion of the descender <NUM>. To define the opening <NUM>, the mask layer <NUM> is patterned and opening <NUM> is formed in the device layer <NUM> of the second wafer <NUM>, e.g., using standard microfabrication techniques including lithography and etching. For instance, a layer of resist can be deposited onto the unpatterned mask layer <NUM> and lithographically patterned. The mask layer <NUM> can be etched to form openings through the mask layer <NUM>. Then the device layer <NUM> can be etched using the mask layer <NUM> as the mask.

An opening <NUM> can be formed, by a similar or the same process, entirely through the mask layer <NUM> and the device layer <NUM> to provide a portion of the return channel <NUM> (step <NUM>).

In addition, a recessed area <NUM> can be formed in the top surface of the device layer <NUM> between the opening <NUM> and the opening <NUM> to provide the outlet passage <NUM> (step <NUM>). The recessed area <NUM> can extend partially, but not entirely, through the device layer <NUM>, leaving a portion 88a of the device layer <NUM> below the recessed area <NUM>. Thus, the openings <NUM> and <NUM> can be deeper than the recessed area <NUM>. Alternatively, the recessed area <NUM> can extend entirely through the device layer <NUM>.

Referring to <FIG> and <FIG>, the second wafer <NUM> is bonded to the first wafer <NUM> (step <NUM>), e.g., using thermal bonding or another wafer bonding technique) to form an assembly <NUM>. In particular, the second wafer <NUM> is bonded to the first wafer <NUM> such that the mask layer side of the first wafer <NUM> is in contact with the mask layer side of the second wafer <NUM>. The opening <NUM> can align with the opening that will provide the nozzle <NUM>. Thus, the mask layer <NUM> can be bonded to the mask layer <NUM>. In some implementations, the mask layer <NUM> and/or the mask layer <NUM> is removed before the second wafer <NUM> is bonded to the first wafer <NUM>.

The passage formed recessed area <NUM> between the top of the second wafer <NUM> and the portion 88a of the device layer <NUM> provides the outlet passage <NUM>.

The etch stop layer <NUM> covers the recess <NUM>. Thus, the etch stop layer <NUM> can provide the membrane <NUM> and define the cavity <NUM>. Although only one recess <NUM> is shown in <FIG>, there can be multiple recesses so as to form multiple cavities <NUM>. In addition, although the cavity <NUM> shown in <FIG> is below the return channel <NUM>, similar cavities can be formed in addition or alternatively below the supply channel <NUM> by forming the recesses in the appropriate locations.

Referring to <FIG> and <FIG>, the handle layer <NUM> of the second wafer <NUM> is removed (step <NUM>), e.g., by grinding and polishing, wet etching, plasma etching, or another removal process, leaving the etch stop layer <NUM> and the device layer <NUM>.

Referring to <FIG> and <FIG>, holes <NUM> are etched through the etch stop layer <NUM> (step <NUM>). The portion of the etch stop layer <NUM> with the holes <NUM> thus forms the filter feature that is positioned close to the nozzle <NUM> and in the flow path of fluid to the nozzle. In addition, a hole is etched through the etch stop layer <NUM> above the opening <NUM>. This exposes the opening <NUM> that will be the lower portion of the return channel <NUM>.

The approach of <FIG> allows some control over the relative thickness of the membranes <NUM> and <NUM>. That is, the membrane <NUM> and membrane <NUM> need not have the same thickness and/or composition, and the thickness and/or composition of each membrane can thus be selected for different purposes.

The wafer assembly <NUM> having nozzles <NUM>, optional recesses <NUM> formed in the device layer <NUM>, and a membrane <NUM> positioned close to the nozzles can be further processed, e.g., as described in <CIT>, to form the fluid ejectors <NUM> of the printhead <NUM>.

For instance, referring to <FIG> and <FIG>, in some examples, a top surface <NUM> of the assembly <NUM>, e.g., the exposed surface of the etch stop layer <NUM>, can be bonded to a flow path wafer <NUM> (step <NUM>). For instance, the top face <NUM> of the first wafer <NUM> can be bonded to the flow path wafer <NUM> using low-temperature bonding, such as bonding with an epoxy (e.g., benzocyclobutene (BCB)) or using low-temperature plasma activated bonding.

The flow path wafer <NUM> can be fabricated before bonding to have portions of the flow passages <NUM>, such as supply channel <NUM>, chamber inlet passage <NUM>, pumping chamber <NUM>, a portion of descender <NUM> (with the remainder provided by opening <NUM>), and a portion of outlet feed channel <NUM> (with the remainder provided by opening <NUM>). Other elements such as actuators (not shown) can be formed before or after the assembly <NUM> is bonded to the flow path wafer <NUM>.

Referring to <FIG> and <FIG>, the handle layer <NUM> can then be removed (step <NUM>), e.g., by grinding and polishing, wet etching, plasma etching, or another removal process. The etch stop layer <NUM>, if present, is either removed (as shown in <FIG>) or masked and etched, e.g., using standard microfabrication techniques including lithography and etching, to expose the nozzles (step <NUM>).

After the actuator is formed or attached, the resulting substrate generally corresponds to the substrate shown in <FIG>, although the bottom surface of the membrane <NUM> is spaced slightly above (by the thickness of the portion 88a) the intersection between the descender <NUM> and the outlet passage <NUM>. On the other hand, if the recess <NUM> extends entirely through the device layer <NUM>, then the bottom surface of the membrane <NUM> would be coplanar with the top surface of the outlet passage <NUM>.

In the implementation shown in <FIG>, the outlet passage <NUM> is provided by the recess <NUM> in the device layer <NUM> rather than a recess in the wafer <NUM>. Alternatively, the outlet passage <NUM> could be provided by a recess in the bottom surface of the flow path wafer <NUM> rather than the device layer <NUM>. In this case, which is similar to <FIG>, the top surface of the etch stop layer <NUM> provides the bottom surface of the outlet passage <NUM>.

13A-<NUM> illustrate a process similar to that of <FIG> of fabricating the body <NUM> and nozzle layer <NUM> of the substrate <NUM>. However, in this example, the holes <NUM> can pass through some or all of the device layer <NUM>. Fabrication can proceed generally as described above for <FIG>, except as noted below.

In particular, referring to <FIG>, rather than create an aperture <NUM> entirely through the device layer <NUM>, a recessed area <NUM> is formed where the nozzle <NUM> will be located. This recessed area <NUM> can be the same depth as the recessed area <NUM> that will provide the outlet passage <NUM>, or deeper. As shown by <FIG> this leaves a thin portion 88b of the device layer <NUM> that will overlie the nozzle <NUM> when the first wafer is bonded to the second wafer.

Referring to <FIG>, after openings are formed in the etch stop layer <NUM>, the etch stop layer <NUM> can be used as a mask, and openings can be etched through the thin portion 88b of the device layer <NUM>, e.g., by reactive ion etching, until the recess <NUM> is exposed. The resulting openings through both the etch stop layer <NUM> and the thin portion 88b of the device layer <NUM> provide the holes <NUM> through the membrane. Fabrication can then proceed as shown in <FIG>. An advantage of this approach is that it permits selection of the thickness of the membrane <NUM>.

After the actuator is formed or attached, the resulting substrate generally corresponds to the substrate shown in <FIG>. If the recessed area <NUM> has the same depth as the recessed area <NUM>, then the bottom surface of the membrane <NUM> will be coplanar with the top surface of the outlet passage <NUM>.

<FIG> show another example approach to fabricating the body <NUM> and nozzle layer <NUM> of the substrate <NUM>. In this example, the substrate is fabricated to have fluid ejectors <NUM> with a membrane <NUM> in the outlet passage <NUM>. In particular, the membrane <NUM> can be in the outlet passage <NUM> at a position spaced away from both the descender <NUM> and the return channel <NUM>. The membrane can provide the impedance structure <NUM>.

The substrate can also include compliant microstructures that include one or more cavities <NUM> formed in the nozzle layer <NUM>. Fluid ejectors <NUM> having only the membrane <NUM> can be fabricated according to a similar approach. For example, to fabricate a fluid ejector without the cavities <NUM>, one can simply omit the portions of the steps associated with formation of the recess <NUM> illustrated by <FIG>.

Referring to <FIG> and <FIG>, a first wafer <NUM> (e.g., a silicon wafer or a silicon-on-insulator (SOI) wafer) provides a nozzle wafer. The first wafer <NUM> includes a mask layer <NUM> (e.g., an oxide or nitride mask layer, such as SiO2 or Si3N4), a device layer <NUM> (e.g., a silicon device layer <NUM>), an etch stop layer <NUM> (e.g., an oxide or nitride etch stop layer), and a handle layer <NUM> (e.g., a silicon handle layer). In some examples, the first wafer <NUM> does not include the etch stop layer <NUM>. In some examples, e.g., when the first wafer <NUM> is an SOI wafer, the insulator layer of the SOI wafer <NUM> acts as the etch stop layer <NUM>.

To define the cavities <NUM>, the mask layer <NUM> is patterned and recesses <NUM> are formed in the device layer <NUM> of the second wafer <NUM> (step <NUM>), e.g., using standard microfabrication techniques including lithography and etching. Although <FIG> illustrates the recess <NUM> as extending entirely through the device layer <NUM>, this is not necessary; the recess <NUM> can extend only partially through the device layer <NUM>.

An opening is formed in the mask layer <NUM> and optionally a recess <NUM> is formed at least partially through the device layer <NUM>, e.g., using standard microfabrication techniques including lithography and etching. This recess <NUM> will be below the outlet passage <NUM>, and could be considered to provide a portion of the descender <NUM> or the nozzle <NUM>. <FIG> illustrates the recess <NUM> as an opening extending entirely through the device layer <NUM>, but this is not necessary; the recess <NUM> can extend only partially through the device layer <NUM>.

Similarly, an opening is formed in the mask layer <NUM> and a recess <NUM> is formed at least partially through the device layer <NUM> (step <NUM>). This recess will provide a portion of the outlet passage <NUM>. <FIG> illustrates the recess <NUM> as extending entirely through the device layer <NUM>, but is not necessary; the recess <NUM> can extend only partially through the device layer <NUM>. However, the recess <NUM> should be at least as deep as the recess <NUM>.

The recess <NUM> (if present), opening <NUM> and recess <NUM> can be formed simultaneously in a single etching step. In this case, the recess <NUM> (if present), opening <NUM> and recess <NUM> would all have the same depth. For example, a layer of resist can be deposited onto the unpatterned mask layer <NUM> and lithographically patterned. The mask layer <NUM> can be etched to form openings through the mask layer <NUM>. Then the device layer <NUM> can be etched using the mask layer <NUM> as the mask.

On the other hand, to provide the recess <NUM> (if present), opening <NUM> and recess <NUM> with different depths, multiple etching steps can be used. For example, for each feature a layer of resist can be deposited and lithographically patterned, and the substrate then subjected to an etching step (the resist can cover previously defined features to protect them from subsequent etching steps). In some implementations, the photoresist itself can be used as the mask.

Referring to <FIG> and <FIG>, the second wafer <NUM> is bonded to the first wafer <NUM> (step <NUM>), e.g., using thermal bonding or another wafer bonding technique, to form an assembly <NUM>. In particular, the second wafer <NUM> is bonded to the first wafer <NUM> such that the mask layer side of the first wafer <NUM> is in contact with the mask layer side of the second wafer <NUM>. Thus, the mask layer <NUM> can be bonded to the mask layer <NUM>. In some implementations, the mask layer <NUM> and/or the mask layer <NUM> is removed before the second wafer <NUM> is bonded to the first wafer <NUM>. The opening <NUM> can align with the opening that will provide the nozzle <NUM>. When the recess <NUM> is covered by the etch stop layer <NUM> if forms the cavity <NUM>.

Referring to <FIG> and <FIG>, holes <NUM> are etched through the etch stop layer <NUM> until the recess <NUM> is reached (step <NUM>) to form the impedance feature <NUM>. The holes <NUM> can be formed by an etching process such as wet etching or plasma etching. In particular, the holes <NUM> can be formed by an anisotropic etch, e.g., a reactive ion etch.

In addition, an aperture <NUM> can be formed through the etch stop layer <NUM> until the recess <NUM> is reached to provide an opening between the outlet passage <NUM> and the return channel <NUM> (step <NUM>).

In addition, an aperture <NUM> can be formed through the etch stop layer <NUM> until the recess <NUM> is reached to provide an opening between the descender <NUM> and the nozzle <NUM>.

The openings <NUM>, opening <NUM> and opening <NUM> can be formed simultaneously in a single etching step. In particular, the openings can be formed by an anisotropic etch, e.g., a reactive ion etch.

Referring to <FIG>, if the recess <NUM> did not extend entirely through the device layer <NUM>, then a further etching step can be performed, e.g., using the etch stop layer <NUM> as a mask. Openings <NUM> and <NUM> can be etched through a thin portion 88c of the device layer <NUM> above the recess <NUM>, e.g., by reactive ion etching, until the recess <NUM> is exposed. An advantage of this approach is that it permits selection of the thickness of the membrane <NUM>, e.g., by selecting the depth of the recess <NUM>. The aspect shown in <FIG> can be combined with the various alternatives.

Assuming that the recess <NUM> extends entirely through the device layer <NUM> as shown in <FIG>, then the portion of the etch stop layer <NUM> spanning the flow path <NUM> provides the membrane <NUM>. On the other hand, if the recess <NUM> extends only partially through the device layer <NUM> as shown in <FIG>, then the combination of the etch stop layer <NUM> and the thin portion 88c of the device layer <NUM> provide the membrane <NUM>.

In the approach of <FIG>, the device layer <NUM>, the mask layers <NUM>, <NUM> (if present), the device layer <NUM> and the etch stop layer <NUM> can provide the nozzle layer <NUM>. The approach of <FIG> provides a thick, robust nozzle layer <NUM> that is not thinned by the fabrication of the membrane <NUM>. The resulting assembly <NUM> with cavity <NUM> and/or membrane <NUM>, can be further processed to form the fluid ejectors <NUM> of the printhead.

For instance, referring to <FIG>, a top surface <NUM> of the assembly <NUM>, e.g., the exposed surface of the etch stop layer <NUM>, can be bonded to a flow path wafer <NUM> (step <NUM>). The flow path wafer <NUM> can be fabricated before bonding to have the flow passages <NUM>, such as supply channel <NUM>, chamber inlet passage <NUM>, pumping chamber <NUM>, descenders <NUM>, a portion of outlet passage <NUM>, and outlet feed channel <NUM>. For instance, the top face <NUM> of the first wafer <NUM> can be bonded to the flow path wafer <NUM> using low-temperature bonding, such as bonding with an epoxy (e.g., benzocyclobutene (BCB)) or using low-temperature plasma activated bonding. Other elements such as actuators (not shown) can be formed before or after the assembly <NUM> is bonded to the flow path wafer <NUM>.

In the implementation shown in <FIG>, one portion of the outlet passage <NUM> is provided by the recess <NUM> in the device layer <NUM>, and another portion of the outlet passage <NUM> is provided by a recess <NUM> in the bottom of the flow path wafer <NUM>. The recess <NUM> in the bottom can extend from the descender <NUM>. The recess <NUM> and the recess <NUM> overlap across the holes <NUM>, so that the resulting membrane <NUM> divides the outlet passage <NUM> into a first region 26a above the membrane <NUM> and a second region 26b below the membrane.

Although the implementation shown in <FIG> has the upper portion 26a of the outlet passage <NUM> connected to the descender <NUM> and the lower portion 26b of the outlet passage connected to the return channel <NUM>, this could be reversed as shown in <FIG>. For example, the recess <NUM> in the bottom of the flow path wafer <NUM> could extend from return channel <NUM>, rather than the descender <NUM>, to the openings <NUM>. In addition, the recess <NUM> could be joined to (and be considered part of) the opening <NUM>. Thus, the recess <NUM> can extend from the descender <NUM> to the opening <NUM>.

Moreover, the implementation shown in <FIG> could be combined with various other aspects. For example, as shown in <FIG>, the recess <NUM> can be formed so that it extends only partially through the device layer <NUM>, and a further etching step can be performed, e.g., using the etch stop layer <NUM> as a mask. Thus, openings <NUM> are etched through a thin portion 88d of the device layer <NUM> above the recess <NUM>, e.g., by reactive ion etching, until the recess <NUM> is exposed. As a result, the combination of the etch stop layer <NUM> and the thin portion 88c of the device layer <NUM> provide the membrane <NUM> of the impedance feature <NUM>.

Referring to <FIG> and <FIG>, after bonding, the handle layer <NUM> and etch stop layer <NUM> can be removed (step <NUM>), e.g., by grinding and polishing, wet etching, plasma etching, or another removal process, to expose the nozzles <NUM>. In some implementations, the etch stop layer <NUM> is not removed, but apertures are formed through the etch stop layer <NUM> to complete the nozzles (step <NUM>). After the actuator is formed or attached, the resulting substrate generally corresponds to the substrate shown in <FIG>.

As shown in <FIG>, the same layer <NUM> can provide the membrane <NUM> for the compliant microstructure (if present) and the membrane <NUM>. Also as shown in <FIG>, with the outlet passage <NUM> formed as a recess in the bottom of the flow path wafer <NUM>, the top surface <NUM> of the assembly <NUM> of the first and second wafers can provide the lower surface of the outlet passage <NUM>. In addition, the top surface of the membrane <NUM> can be coplanar with the lower surface of the outlet passage <NUM>. Similarly, the top surface of the membrane <NUM> can be coplanar with the lower surface of the return channel <NUM>.

<FIG> illustrate a process similar to that of <FIG> of fabricating the body <NUM> and nozzle layer <NUM> of the substrate <NUM>. However, in this example, the openings <NUM> are located immediately below the return channel <NUM> rather than within the outlet passage <NUM>. Fabrication can proceed generally as described above for <FIG> and <FIG>, except as noted below.

Referring to <FIG>, a first recess <NUM> is formed in the device layer <NUM> in a region corresponding to the nozzle <NUM>. This recess <NUM> will be below the outlet passage <NUM>, and could be considered to provide a portion of the descender <NUM> or the nozzle <NUM>. A second recess <NUM> is formed in the device layer <NUM> in the region that will underlie a portion of the return channel <NUM>. These recesses <NUM> and <NUM> can be formed by patterning the mask layer <NUM> and using it as a mask for etching the device layer <NUM>.

In addition, referring to <FIG>, a third recess <NUM> in the device layer <NUM> to connect the first recess <NUM> and the second recess <NUM>. A portion 88e of the device layer <NUM> can remain below recess <NUM>. The recess <NUM> can be formed by patterning the mask layer <NUM> and using it as a mask for etching the device layer <NUM>. Optionally the mask layer <NUM> can be stripped from the entire wafer <NUM>.

Although <FIG> illustrate the recess <NUM> and the recess <NUM> as openings extending entirely through the device layer <NUM>, this is not necessary. The recess <NUM> and/or the recess <NUM> can extend only partially through the device layer <NUM>. However, the recess <NUM> should at least as deep (i.e., the same or greater depth) as the recess <NUM>. Similarly, although <FIG> illustrates the recess <NUM> as extending only partially through the device layer <NUM>, this is not necessary. The recess <NUM> can extend entirely through the device layer <NUM>. Where the recesses <NUM>, <NUM>, <NUM> are the same depth, they can be formed simultaneously in a single etching step. The relative depths of the recesses can be selected based on the needs for the height of the outlet passage <NUM> and thickness of the membrane <NUM>, e.g., based desired resistance to fluid flow.

<FIG> proceeds similarly to <FIG>, with the first wafer <NUM> bonded to the second wafer <NUM> to form an assembly <NUM> and the opening <NUM> aligning to the nozzle <NUM>. <FIG> proceeds similarly to <FIG>, in which the handle layer <NUM> is removed.

Referring to <FIG>, holes <NUM> are etched through the etch stop layer <NUM> until the recess <NUM> is reached to form the impedance feature <NUM>. The holes <NUM> can be formed by an etching process such as wet etching or plasma etching. In particular, the holes <NUM> can be formed by an anisotropic etch, e.g., a reactive ion etch.

The openings <NUM> and opening <NUM> can be formed simultaneously in a single etching step. In particular, the openings can be formed by an anisotropic etch, e.g., a reactive ion etch.

If the recess <NUM> did not extend entirely through the device layer <NUM>, then a further etching step can be performed, e.g., using the etch stop layer <NUM> as a mask. Similarly, if the recess <NUM> did not extend entirely through the device layer <NUM>, then a further etching step can be performed, e.g., using the etch stop layer <NUM> as a mask. Thus, openings <NUM> and <NUM> can be etched through the thin portion 88e of the device layer <NUM>, e.g., by reactive ion etching, until the recess <NUM> is exposed.

Assuming that the recess <NUM> extends entirely through the device layer <NUM> as shown in <FIG>, then the portion of the etch stop layer <NUM> between the outlet passage <NUM> and the return channel <NUM> provides the membrane <NUM>. On the other hand, if the recess <NUM> extends only partially through the device layer <NUM> (e.g., in a manner equivalent to what is shown in <FIG>), then the combination of the etch stop layer <NUM> and the thin portion 88e of the device layer <NUM> provides the membrane <NUM>.

Referring to <FIG>, a top surface <NUM> of the assembly <NUM>, e.g., the exposed surface of the etch stop layer <NUM>, can be bonded to a flow path wafer <NUM>. <FIG> proceeds similarly to <FIG>, but the flow path wafer <NUM> does not have any recess that defines the outlet passage <NUM>, as it is defined entirely in the device layer <NUM>.

<FIG> proceeds similarly to <FIG>, in which the handle layer <NUM> and etch stop layer <NUM> are removed or the handle layer <NUM> is removed and apertures are formed through the etch stop layer <NUM> to complete the nozzles. After the actuator is formed or attached, the resulting substrate generally corresponds to the substrate shown in <FIG>.

Referring to <FIG>, in some implementations, a mask <NUM> including multiple openings <NUM>, e.g., rectangular openings, can be used to define the holes <NUM> of a desired size for the membrane <NUM>. Each opening <NUM> corresponds to a cell region <NUM> defined by the corners of the opening <NUM>, and the size and orientation of the openings <NUM> cause adjacent cell regions <NUM> to overlap. The area of each cell region <NUM> is approximately the square of the length of the long side l of the corresponding opening <NUM>. With an anisotropic etch process (e.g., a potassium hydroxide etch process), correctly sized holes can be fabricated by continuing the anisotropic etch until a termination crystal plane (e.g., a <<NUM>> plane) is reached. For instance, the corners of each opening <NUM> can be positioned to expose a <<NUM>> plane, such that each opening <NUM> will cause the region defined by its corresponding cell region <NUM> to be etched. Since adjacent cell regions <NUM> overlap, the entire area can be opening by this etch process.

In some examples, a thick layer <NUM> can be used (e.g., <NUM>, <NUM>, or <NUM> thick). The use of a thick nozzle wafer minimizes the risk that the nozzle fabrication process will thin the nozzle wafer to an extent that the nozzle wafer is weakened.

The particular flow path configuration of the channel <NUM>, inlet passage <NUM> and pumping chamber <NUM> that is common to the various implementations is merely one example of a flow path configuration. The approach for the filter feature or impedance feature described below can be used in many other flow path configurations. For example, if the supply channel <NUM> is located at the same level as the pumping chamber <NUM>, then the ascender 16a is unnecessary. As another example, additional horizontal passages could be positioned between the pumping chamber <NUM> and the nozzle <NUM>. In general, discussion of the descender can be generalized to a first passage that connects a pumping chamber to an entrance of the nozzle, and discussion of the outlet passage can be generalized to a second passage that connects the entrance of the nozzle to the return channel.

Indications of the various elements as first or second, e.g., the first wafer and the second wafer, do not necessarily indicate the order in which the elements are fabricated. Although terms of positioning such as "above" and "below" are used, these terms are used to indicate relative positioning of elements within the system, and do not necessarily indicate position relative to gravity.

Claim 1:
A fluid ejector (<NUM>) comprising:
a nozzle layer (<NUM>) having an outer surface, and inner surface, and a nozzle (<NUM>) extending between the inner surface and the outer surface, the nozzle (<NUM>) having an entrance at the inner surface to receive fluid and an exit opening at an outer surface for ejection of fluid;
a body (<NUM>) to which the inner surface of the nozzle layer (<NUM>) is secured, the body (<NUM>) including a pumping chamber (<NUM>), a return channel (<NUM>), a first passage (<NUM>) fluidically connecting the pumping chamber (<NUM>) to the entrance of the nozzle (<NUM>), and a second passage (<NUM>) fluidically connecting the entrance of the nozzle (<NUM>) to the return channel (<NUM>);
an actuator (<NUM>) configured to cause fluid to flow out of the pumping chamber (<NUM>) such that actuation of the actuator (<NUM>) causes fluid to be ejected from the nozzle (<NUM>);
a first membrane (<NUM>) disposed between the actuator (<NUM>) and the pumping chamber (<NUM>) and isolating the actuator (<NUM>) from fluid in the pumping chamber (<NUM>); and
a second membrane (<NUM>) different from the first membrane, the second membrane formed across and partially blocking the entrance of the nozzle (<NUM>) , the second membrane (<NUM>) having at least one hole (<NUM>) therethrough such that in operation of the fluid ejector (<NUM>) fluid flows through the at least one hole (<NUM>) in the second membrane (<NUM>).