Controller for high throughput dispenser

Abstract

(Figure 2(a)) The present disclosure provides a controller for a pump assembly (100). The pump assembly comprises: a substrate (102) having a first surface (104) and an opposite second surface (106); a plurality of layers (108) on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator (112) providing a piezoelectric body (118) and first and second electrodes (116, 120) in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion (124); and at least one pump passage (126) defined by the pump assembly. The controller is configured to cause a first driving signal to be received at the piezoelectric actuator at a first time and cause a second driving signal to be received at the piezoelectric actuator at a second time, after the first time. The piezoelectric actuator is configured to cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage. The piezoelectric actuator is further configured to cause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage. In this aspect, the time between the first time and the second time is less than the time from the first time in which the moveable portion would naturally come to rest after the movement caused in response to receipt of the first driving signal at the piezoelectric actuator, and more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the second time, would be in the same direction as the movement of the moveable portion caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary at the second time.

Description

[0001] CONTROLLER FOR HIGH THROUGHPUT DISPENSER

[0002] Field of the invention

[0003] The present inventions relate to a controller for a pump assembly and a method of pumping a liquid.

[0004] Background to the invention

[0005] It is known that ejecting a droplet of liquid of predetermined volume from a droplet ejector having a piezoelectric actuator may be achieved by applying a driving pulse to the piezoelectric actuator to cause oscillation of a membrane. The droplet ejection rate of these typical “droplet on demand” systems is limited as a wait period is required between ejections for the membrane to stop oscillating and for the nozzles to refill by capillary action. This priming of the nozzles is necessary to produce droplets of consistent and predetermined volume. This wait period also requires each driving pulse to have a sufficiently large amplitude to cause movement of an at-rest membrane sufficient to eject a droplet.

[0006] It is in this context that the present inventions have been devised.

[0007] Summary of the inventionIn accordance with a first aspect of the present invention, there is provided a method of pumping a liquid, the method comprising providing a pump assembly. The pump assembly comprises: a substrate having a first surface and an opposite second surface; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to a controller, and wherein the plurality of layers comprises a moveable portion; and at least one pump passage defined by the pump assembly. The method further comprises causing a first volume of the liquid to be pumped via the at least one pump passage in response to receipt of a first driving signal at the piezoelectric actuator causing movement of the moveable portion; and causing a second volume of the liquid to be pumped via the at least one pump passage in response to receipt of a second driving signal at the piezoelectric actuator causing movement of the moveable portion. In this aspect, the second driving signal is received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator, and more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the time at which the second driving signal is received at the piezoelectric actuator, would be in the same direction as would be caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.

[0008] It may be that the second driving signal is received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator with an amplitude greater than 5% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator.

[0009] It will be understood that the amplitude of the movement of the moveable portion is the magnitude of the maximum displacement of the moveable portion from an equilibrium position. For damped movement, the amplitude of the movement of the moveable portion will decrease with time from an initial maximum amplitude.In accordance with a second aspect of the present invention, there is provided a controller for a pump assembly. The pump assembly comprises: a substrate having a first surface and an opposite second surface; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; and at least one pump passage defined by the pump assembly. The controller is configured to cause a first driving signal to be received at the piezoelectric actuator at a first time and cause a second driving signal to be received at the piezoelectric actuator at a second time, after the first time. The piezoelectric actuator is configured to cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage. The piezoelectric actuator is further configured to cause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage. In this aspect, the time between the first time and the second time is less than the time from the first time in which the moveable portion would naturally come to rest after the movement caused in response to receipt of the first driving signal at the piezoelectric actuator, and more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the second time, would be in the same direction as the movement of the moveable portion caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary at the second time.

[0010] The present disclosure extends to a method and a controller without the requirement that more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the time at which the second driving signal is received at the piezoelectric actuator, would be in the same direction as would be caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.It may be that the time between the first time and the second time is less than the time from the first time in which the amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator would naturally fall to below 5% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator.

[0011] The present invention extends to the pump assembly, comprising the controller.

[0012] It will be understood that more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator being in the same direction as the movement of the moveable portion caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary at the second time means that, for more than 50% of the time after the second time in which the moveable portion would be moving in response to receipt of the first driving signal at the piezoelectric actuator, the direction of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator would be in the same direction as the movement caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary at the second time.

[0013] Thus, at least some of the movement of the moveable portion remaining after the first volume of the liquid has been pumped will be conserved when the second driving signal is received at the piezoelectric actuator, and is then used when pumping the second volume of the liquid. As such, the same amount of movement can be caused, and the same volume of the liquid pumped, with a lower energy second driving signal than would be required by known piezoelectric pumping systems which receive the second driving signal when the moveable portion has come to rest. Thus, a more energy-efficient means of pumping the same volume of the liquid is achieved. Furthermore, by not having to wait until the moveable portion has come to rest, the volumetric flow rate of the liquid from the pump assembly is increased.

[0014] It may be that at least some of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator causes the second volume of the liquid to be pumped via the at least one pump passage.The movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the time at which the second driving signal is received at the piezoelectric actuator, will be understood to be the movement that the moveable portion would continue to have had as a result of the first driving signal, as taken from the point in time when the second signal is received at the piezoelectric actuator, had the second driving signal not been received at the piezoelectric actuator at that point. In the absence of receipt of the second driving signal at that point in time, the moveable portion would continue to move as a result of receipt of the first driving signal after that point in time. In this aspect of the present invention, more than 50% of this movement is in the same direction as that which would be caused were the moveable portion not to be moving when the second driving signal is received at the piezoelectric actuator.

[0015] The term pump will be understood to mean any use of the piezoelectric actuator to cause movement of the liquid via the at least one pump passage. The pump assembly may be considered a micropump due to the relatively small volumes of the liquid that are moved via the at least one pump passage.

[0016] It may be that more than 75%, for example more than 80%, optionally more than 90%, optionally more than 95%, optionally more than 99%, of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the time at which the second driving signal is received at the piezoelectric actuator, would be in the same direction as would be caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator. It may be that more than 75%, for example more than 80%, optionally more than 90%, optionally more than 95%, optionally more than 99%, of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the second time, would be in the same direction as would be caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.Thus, even more of the movement of the moveable portion remaining after the first volume of the liquid has been pumped will be conserved and used to pump the second volume of the liquid, leading to even greater energy efficiency for the same volume of the liquid pumped.

[0017] The second driving signal may be received at the piezoelectric actuator when the moveable portion is moving, in response to receipt of the first driving signal at the piezoelectric actuator, in the same direction as the movement which would be caused in response to receipt of an initial portion of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.

[0018] The controller may be configured to cause the second driving signal to be received at the piezoelectric actuator when the moveable portion is moving in response to receipt of the first driving signal at the piezoelectric actuator in the same direction as the movement which would be caused in response to receipt of an initial portion of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.

[0019] That is, if the initial portion of the second driving signal, when received at the piezoelectric actuator, causes the moveable portion to move in a particular direction, then the second driving signal is received, or the controller is configured to cause the second driving signal to be received, at the piezoelectric actuator when the moveable portion is moving in that same direction.

[0020] Thus, the movement of the moveable portion, as caused by the first driving signal, is not interrupted or disturbed upon receipt of the second driving signal; the second driving signal, when received, will not cause a change in the direction of motion of the moveable portion. Thus, this residual movement can be used in the pumping of the second volume of the liquid. Thus, less energy is required to pump each volume of the liquid than in typical piezoelectric pumping systems, as the movement of the moveable portion is retained to be used in each subsequent pumping action. Additionally, the amplitude of each driving signal can be lower and cause the same volume of the liquid to be pumped compared with typical systems which allow the moveable portion to come to rest before receiving the second driving signal at the piezoelectric actuator.Thus, the energy required per driving signal is reduced as a smaller amount of energy is required to maintain movement of a moveable portion in motion than would be required to cause the same movement of an initially stationary moveable portion.

[0021] The movement of the moveable portion caused in response to receipt of an initial portion of the first driving signal may be in the same direction as the movement caused by the or an initial portion of the second driving signal.

[0022] It will be understood that the movement of the moveable portion after an initial displacement from an equilibrium position, and in the absence of any further disturbance, will tend to be an oscillation of the membrane about the equilibrium position. The membrane, in the absence of a further signal after an initial displacement, will oscillate at the natural frequency of the membrane in operation when in contact with the liquid.

[0023] The difference in time between the time of receipt of the first driving signal at the piezoelectric actuator and the time of receipt of the second driving signal at the piezoelectric actuator may be within half of a period of oscillation of the moveable portion of a multiple of the period of oscillation of the moveable portion. The difference between the first time and the second time may be within half of a period of oscillation of the moveable portion of a multiple of the period of oscillation of the moveable portion. It will be understood that the period of oscillation of the moveable portion is an operational period of oscillation of the moveable portion. That is, the natural period of oscillation of the moveable portion while the pump assembly is in operation, the pump assembly comprising a liquid. The period of oscillation of the moveable portion is typically modified by the liquid.

[0024] The movement of the moveable portion may be an oscillation. The period of the movement of the moveable portion may depend on one or more properties of the liquid, such as the mass of the liquid. The amplitude of the movement of the moveable portion may depend on one or more properties of the liquid, such as the mass of the liquid. The period of the movement of the moveable portion may depend on the mass of the moveable portion. The amplitude of the movement of the moveable portion may depend on the mass of the moveable portion. The period of the movement of the moveable portion may depend on the stiffness of the moveable portion. The amplitudeof the movement of the moveable portion may depend on the stiffness of the moveable portion. The period of the movement of the moveable portion may depend on the stiffness of the plurality of layers. The amplitude of the movement of the moveable portion may depend on the stiffness of the plurality of layers. The period of the movement of the moveable portion may depend on the viscosity of the liquid. The amplitude of the movement of the moveable portion may depend on the viscosity of the liquid.

[0025] The period of the movement of the moveable portion may depend on the thickness of one or more of: the moveable portion, the plurality of layers, the piezoelectric actuator, the piezoelectric body. The period of the movement of the moveable portion may depend on the thickness of one or more of: the moveable portion, the plurality of layers, the piezoelectric actuator, the piezoelectric body.

[0026] The period of oscillation may be at least 0.5 microseconds, for example at least 1 microsecond, optionally at least 1.5 microseconds. The period of oscillation may be at least 4 microseconds. The period of oscillation may be no more than 20 microseconds, for example no more than 15 microseconds, optionally no more than 10 microseconds.

[0027] The difference in time between the time of receipt of the first driving signal at the piezoelectric actuator and the time of receipt of the second driving signal at the piezoelectric actuator may be less than 50 microseconds, for example less than 40 microseconds, for example less than 20 microseconds.

[0028] The second volume of the liquid may be predetermined.

[0029] In accordance with a third aspect of the present invention, there is provided a method of pumping a liquid, the method comprising providing a pump assembly. The pump assembly comprises: a substrate having a first surface and an opposite second surface; a controller; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; and at least one pumppassage defined by the pump assembly. The method further comprises causing a first volume of the liquid to be pumped via the at least one pump passage in response to receipt of a first driving signal at the piezoelectric actuator causing movement of the moveable portion, and causing a second volume of the liquid to be pumped via the at least one pump passage in response to receipt of a second driving signal at the piezoelectric actuator causing movement of the moveable portion. The second driving signal is received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator with an amplitude greater than 5% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, and the second volume of the liquid is predetermined.

[0030] The second driving signal may be received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator with an amplitude greater than 10% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator. The second driving signal may be received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator with an amplitude greater than 20% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator. The second driving signal may be received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator with an amplitude greater than 40% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator.

[0031] In accordance with a fourth aspect of the present invention, there is provided a controller for a pump assembly. The pump assembly comprises: a substrate having a first surface and an opposite second surface; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; and at least one pump passage defined by the pump assembly. The controller is configuredto: cause a first driving signal to be received at the piezoelectric actuator at a first time; and cause a second driving signal to be received at the piezoelectric actuator at a second time, after the first time. The piezoelectric actuator is configured to: cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage; and cause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage. In this aspect, the time between the first time and the second time is less than the time from the first time in which the amplitude of the movement of the moveable portion would naturally fall to below 5% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, and the second volume of the liquid is predetermined.

[0032] The present disclosure extends to a method and a controller without the requirement that the second driving signal is received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator with an amplitude greater than 5% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator.

[0033] The present aspect extends to the pump assembly, comprising the controller.

[0034] Thus, it is possible to produce a known second volume of the liquid within a shorter timescale after the first volume of the liquid has been pumped, compared with known piezoelectric droplet ejectors, as it is not necessary to wait for the system to come to rest. The present inventors have realised that it is possible to operate a pump assembly in such a way that the second volume is predetermined. Previously, the only way to produce multiple known volumes of liquid to be pumped was to allow the system to return to rest, being a known operating condition. The present inventors have realised that this is not necessary.

[0035] It may be that the time between the first time and the second time is less than the time from the first time in which the amplitude of the movement of the moveable portion would naturally fall to below 10% of the maximum amplitude of the movement of themoveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator. It may be that the time between the first time and the second time is less than the time from the first time in which the amplitude of the movement of the moveable portion would naturally fall to below 20% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator. It may be that the time between the first time and the second time is less than the time from the first time in which the amplitude of the movement of the moveable portion would naturally fall to below 40% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator.

[0036] The first driving signal may comprise a first region. The first region is the portion of the first driving signal up to an escape point at which the first volume of the liquid is moving away from the at least one pump passage with sufficient momentum to continue progressing away from the pump assembly in the absence of any further driving signal. The second driving signal may be received, or the controller may cause the second driving signal to be received at the piezoelectric actuator within a settling time of the escape point of the first driving signal. The settling time of the first driving signal is the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 5% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator. The second volume of the liquid may be predetermined.

[0037] In accordance with a fifth aspect of the present invention, there is provided a method of pumping a liquid, the method comprising providing a pump assembly. The pump assembly comprises: a substrate having a first surface and an opposite second surface; a controller; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; and at least one pump passage defined by the pump assembly. The method further comprises: causing a firstvolume of the liquid to be pumped via the at least one pump passage in response to receipt of a first driving signal at the piezoelectric actuator causing movement of the moveable portion; and causing a second volume of the liquid to be pumped via the at least one pump passage in response to receipt of a second driving signal at the piezoelectric actuator causing movement of the moveable portion. The first driving signal comprises a first region up to an escape point at which the first volume of the liquid is moving away from the at least one pump passage with sufficient momentum to continue progressing away from the pump assembly in the absence of any further driving signal. The second driving signal is received at the piezoelectric actuator within a settling time of the escape point of the first driving signal. The settling time of the first driving signal is the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 5% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator. The second volume of the liquid is predetermined.

[0038] In accordance with a sixth aspect of the present invention, there is provided a controller for a pump assembly. The pump assembly comprises: a substrate having a first surface and an opposite second surface; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; and at least one pump passage defined by the pump assembly. The controller is configured to: cause a first driving signal to be received at the piezoelectric actuator at a first time; and cause a second driving signal to be received at the piezoelectric actuator at a second time, after the first time. The piezoelectric actuator is configured to: cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage; and cause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage. The first driving signal comprises a first region up to an escape point at which the firstvolume of the liquid is moving away from the at least one pump passage with sufficient momentum to continue progressing away from the pump assembly in the absence of any further driving signal. The controller causes the second driving signal to be received at the piezoelectric actuator within a settling time of the escape point of the first driving signal, wherein the settling time of the first driving signal is the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 5% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator. The second volume of the liquid is predetermined.

[0039] The present aspect extends to the pump assembly, comprising the controller.

[0040] Thus, it is possible to produce a known second volume of the liquid within a shorter timescale after the first volume of the liquid has been pumped, compared with known piezoelectric droplet ejectors. Previously, for predictable, known volumes to be pumped subsequent to an initial volume, it was necessary to wait until the system naturally came to rest following the first driving signal that caused the first volume of the liquid to be pumped. The present inventors have realised that waiting is unnecessary, and are able to determine the second volume even when the system would not have naturally come to rest following receipt of enough of the first driving signal to cause the first volume to be pumped.

[0041] The settling time of the first driving signal may be the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 10% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator.

[0042] The settling time of the first driving signal may be the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at thepiezoelectric actuator to naturally fall to below 20% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator.

[0043] The settling time of the first driving signal may be the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 40% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator.

[0044] It may be that the first driving signal comprises a further region after the first region. Typically that further region is substantially incapable of affecting the volume or velocity of the first volume of the liquid.

[0045] The second driving signal may be received at the piezoelectric actuator within 90% of the settling time from the escape point of the first driving signal. The second driving signal may be received at the piezoelectric actuator within 80%, for example within 75%, of the settling time from the escape point of the first driving signal. The second driving signal may be received at the piezoelectric actuator within 50% of the settling time from the escape point of the first driving signal. The second driving signal may be received at the piezoelectric actuator within 20% of the settling time from the escape point of the first driving signal. The second driving signal may be received at the piezoelectric actuator within 10%, for example within 5%, of the settling time from the escape point of the first driving signal.

[0046] The controller may cause the second driving signal to be received at the piezoelectric actuator within 90% of the settling time from the escape point of the first driving signal. The controller may cause the second driving signal to be received at the piezoelectric actuator within 80%, for example within 75%, of the settling time from the escape point of the first driving signal. The controller may cause the second driving signal to be received at the piezoelectric actuator within 50% of the settling time from the escape point of the first driving signal. The controller may cause the second driving signal tobe received at the piezoelectric actuator within 20% of the settling time from the escape point of the first driving signal. The controller may cause the second driving signal to be received at the piezoelectric actuator within 10%, for example within 5%, of the settling time from the escape point of the first driving signal.

[0047] The second driving signal may be received at the piezoelectric actuator at the escape point of the first driving signal. The controller may cause the second driving signal to be received at the piezoelectric actuator at the escape point of the first driving signal.

[0048] The first volume of the liquid may be predetermined. The first volume of the liquid may be equal to the second volume of the liquid. That is, the first volume of the liquid may have an equal volume to the second volume of the liquid.

[0049] At least one of the first volume of the liquid and the second volume of the liquid may have a volume of less than 1 x 10'12m3, for example less than 1 x 10'13m3, optionally less than 5 x 10'14m3. At least one of the first volume of the liquid and the second volume of the liquid may have a volume of less than 1 x 10'14m3, for example less than 5 x 10'15m3. At least one of the first volume of the liquid and the second volume of the liquid may have a volume of less than 2 x 10'15m3, for example less than 5 x 10'16m3. At least one of the first volume of the liquid and the second volume of the liquid may have a volume of less than 1 x 10'16m3.

[0050] At least one of the first volume of the liquid and the second volume of the liquid may have a volume greater than 5 x 10'19m3, for example greater than 1 x 10'18m3. At least one of the first volume of the liquid and the second volume of the liquid may have a volume greater than 1 x 10'17m3. At least one of the first volume of the liquid and the second volume of the liquid may have a volume greater than 1 x 10'15m3.

[0051] The present disclosure is intended to disclose any combination of the above-mentioned bounds.

[0052] The first volume of the liquid may form a first droplet. The second volume of the liquid may form a second droplet. The volume of the first droplet may be equal to the volume of the second droplet.The first driving signal and the second driving signal may be amongst a plurality of consecutive driving signals comprised within an actuation signal.

[0053] The actuation signal may be received at the piezoelectric actuator in response to receipt of an activation signal indicative of a demand to pump the liquid via the at least one pump passage.

[0054] The method may further comprise causing the liquid to be pumped via the at least one pump passage in response to receipt of the actuation signal at the piezoelectric actuator causing movement of the moveable portion.

[0055] The controller may cause the actuation signal to be received at the piezoelectric actuator in response to receipt of an activation signal indicative of a demand to pump the liquid via the at least one pump passage.

[0056] The piezoelectric actuator may be configured to cause movement of the moveable portion in response to receipt of the actuation signal at the piezoelectric actuator to thereby cause the liquid to be pumped via the at least one pump passage.

[0057] Receipt of each of the consecutive driving signals at the piezoelectric actuator may be sufficient to cause pumping of the liquid via the at least one pump passage.

[0058] It may be that the liquid is caused to be pumped via the at least one pump passage in response to receipt of the actuation signal at the piezoelectric actuator causing a plurality of movements of the moveable portion. It may be that a plurality of volumes of the liquid are caused to be pumped via the at least one pump passage in response to receipt of the actuation signal at the piezoelectric actuator causing movement of the moveable portion. It may be that a plurality of volumes of the liquid are caused to be pumped via the at least one pump passage in response to receipt of the actuation signal at the piezoelectric actuator causing a plurality of movements of the moveable portion. It may be that each of the plurality of movements of the moveable portion is sufficient to cause pumping of the liquid via the at least one pump passage. It may be that each of the plurality of movements of the moveable portion causes pumping of the liquid via the at least one pump passage. It may be that each of the plurality ofmovements of the moveable portion causes a respective volume of the liquid to be pumped via the at least one pump passage.

[0059] Thus, a continuous stream of droplets may be generated.

[0060] It may be that receipt of each of the consecutive driving signals at the piezoelectric actuator causes movement of the moveable portion. It may be that receipt of each of the consecutive driving signals at the piezoelectric actuator causes a respective volume of the liquid to be pumped via the at least one pump passage. It may be that receipt of each of the consecutive driving signals at the piezoelectric actuator causes a respective movement of a plurality of movements of the moveable portion. It may be that receipt of each of the consecutive driving signals at the piezoelectric actuator causes a respective movement of the moveable portion causing a respective volume of the liquid to be pumped via the at least one pump passage.

[0061] It may be that at least one of the plurality of volumes of the liquid has a predetermined volume. It may be that at least 10% of the plurality of volumes of the liquid has a predetermined volume. It may be that at least 25% of the plurality of volumes of the liquid has a predetermined volume. It may be that at least 50% of the plurality of volumes of the liquid has a predetermined volume. It may be that at least 75% of the plurality of volumes of the liquid has a predetermined volume. It may be that each of the plurality of volumes of the liquid has a predetermined volume.

[0062] It may be that at least one of the plurality of volumes of the liquid is predetermined. It may be that at least 10% of the plurality of volumes of the liquid are predetermined. It may be that at least 25% of the plurality of volumes of the liquid are predetermined. It may be that at least 50% of the plurality of volumes of the liquid are predetermined. It may be that at least 75% of the plurality of volumes of the liquid are predetermined. It may be that each of the plurality of volumes of the liquid are predetermined.

[0063] It may be that at least one of the plurality of volumes of the liquid is equal to at least one other volume of the plurality of volumes of the liquid. It may be that at least half of the plurality of volumes of the liquid have the same volume. It may be that at least 90% of the plurality of volumes of the liquid have the same volume.At least one of the plurality of volumes of the liquid may have a volume of less than 1 x 10-12m3, for example less than 1 x 10'13m3, optionally less than 5 x 10'14m3. At least one of the plurality of volumes of the liquid may have a volume of less than 1 x 10'14m3, for example less than 5 x 10'15m3. At least one of the pluraly of volumes of the liquid may have a volume of less than 2 x 10'15m3, for example less than 5 x 10'16m3. At least one of the plurality of volumes of the liquid may have a volume of less than 1 x 10-16m3.

[0064] At least 50% of the plurality of volumes of the liquid may have a volume of less than 1 x 10-12m3, for example less than 1 x 10'13m3, optionally less than 5 x 10'14m3. At least 50% of the plurality of volumes of the liquid may have a volume of less than 1 x 10'14m3, for example less than 5 x 10'15m3. At least 50% of the plurality of volumes of the liquid may have a volume of less than 2 x 10'15m3, for example less than 5 x 10'16m3. At least 50% of the plurality of volumes of the liquid may have a volume of less than 1 x 10-16m3.

[0065] At least 90% of the plurality of volumes of the liquid may have a volume of less than 1 x 10-12m3, for example less than 1 x 10'13m3, optionally less than 5 x 10'14m3. At least 90% of the plurality of volumes of the liquid may have a volume of less than 1 x 10'14m3, for example less than 5 x 10'15m3. At least 90% of the plurality of volumes of the liquid may have a volume of less than 2 x 10'15m3, for example less than 5 x 10'16m3. At least 90% of the plurality of volumes of the liquid may have a volume of less than 1 x 10-16m3.

[0066] At least one of the plurality of volumes of the liquid may have a volume greater than 5 x 10'19m3, for example greater than 1 x 10'18m3. At least one of the plurality of volumes of the liquid may have a volume greater than 1 x 10'17m3. At least one of the plurality of volumes of the liquid may have a volume greater than 1 x 10'15m3.

[0067] At least 50% of the plurality of volumes of the liquid may have a volume greater than 5 x 10'19m3, for example greater than 1 x 10'18m3. At least 50% of the plurality of volumes of the liquid may have a volume greater than 1 x 10'17m3. At least 50% of the plurality of volumes of the liquid may have a volume greater than 1 x 10'15m3.At least 90% of the plurality of volumes of the liquid may have a volume greater than 5 x 10'19m3, for example greater than 1 x 10'18m3. At least 90% of the plurality of volumes of the liquid may have a volume greater than 1 x 10'17m3. At least 90% of the plurality of volumes of the liquid may have a volume greater than 1 x 10'15m3.

[0068] The first volume of the liquid may form a first droplet of the liquid. The second volume of the liquid may form a second droplet of the liquid. The volume of the first droplet of the liquid may be equal to the volume of the second droplet of the liquid. Each of the plurality of volumes of the liquid may form a respective droplet of the liquid.

[0069] The first volume of the liquid may be a first droplet of the liquid. The second volume of the liquid may be a second droplet of the liquid.

[0070] It may be that causing a volume of the liquid to be pumped via the at least one pump passage causes a respective droplet of the liquid to be formed. It may be that causing a volume of the liquid to be pumped via the at least one pump passage causes a respective droplet of the liquid to be ejected. It may be that causing the first volume of the liquid to be pumped via the at least one pump passage causes a first droplet of the liquid to be formed. It may be that causing the first volume of the liquid to be pumped via the at least one pump passage causes a first droplet of the liquid to be ejected. It may be that causing the second volume of the liquid to be pumped via the at least one pump passage causes a second droplet of the liquid to be formed. It may be that causing the second volume of the liquid to be pumped via the at least one pump passage causes a second droplet of the liquid to be ejected. It may be that causing a plurality of volumes of the liquid to be pumped via the at least one pump passage causes a respective plurality of droplets of the liquid to be formed. It may be that causing a plurality of volumes of the liquid to be pumped via the at least one pump passage causes a respective plurality of droplets of the liquid to be ejected. Thus, it may be that the pump assembly is for ejecting a plurality of droplets of the liquid.

[0071] The controller may comprise control circuitry. The controller may comprise or be an integrated circuit. The controller may comprise CMOS control circuitry.

[0072] The CMOS control circuitry may be formed using conventional CMOS fabrication techniques (e.g. ion implantation, chemical vapour deposition (CVD), physical vapourdeposition (PVD), etching, chemical-mechanical planarization (CMP) and / or electroplating).

[0073] The controller may be configured to output a driving signal. The controller may be configured to output the first driving signal. The controller may be configured to output the second driving signal. The controller may be configured to output the actuation signal.

[0074] The pump assembly may comprise a fluid chamber. The at least one pump passage may be in fluid communication with the fluid chamber. The at least one pump passage may be defined by the plurality of layers. The at least one pump passage may extend through the piezoelectric actuator.

[0075] The plurality of layers may comprise a membrane layer. The membrane layer may be formed on the first surface of the substrate. The piezoelectric actuator may be formed on the membrane layer. The membrane layer may at least partially define the fluid chamber. The membrane layer may at least partially define the at least one pump passage. The membrane layer may define an inner portion of the at least one pump passage.

[0076] The plurality of layers may comprise a protective layer. The protective layer may at least partially define the at least one pump passage. The protective layer may define an outer portion of the at least one pump passage.

[0077] The at least one pump passage may be one pump passage. The at least one pump passage may be at least two pump passages.

[0078] The pump assembly may be configured to maintain a positive pressure of the liquid in the at least one pump passage relative to a pressure external to the pump assembly.

[0079] The pump assembly may further comprise a power source to power the controller and the piezoelectric actuator. The power source typically comprises an energy storage component, such as a battery.The pump assembly may further comprise a connector element for connecting the pump assembly to a further component in fluid communication with the at least one pump passage. Thus, the pump assembly may be configured to connect to other components for supplying the liquid to the at least one pump passage.

[0080] The controller may comprise one or more processors and a memory configured to store instructions which when executed by the one or more processors cause the pump assembly to carry out the functions of the controller described herein. The memory may be non-transitory, computer readable memory. The memory may have the instructions stored thereon. The present invention extends to a non-transitory computer-readable medium (e.g. memory) having the instructions stored thereon to control the pump assembly as described herein. The memory may be solid-state memory. The controller may be provided in a single device. In other examples, the controller may be distributed, having a plurality of processors. A first processor may be separated from a second processor in a distributed manner.

[0081] The at least one pump passage may have a maximum cross-sectional extent of less than 50 x 10'6metres (50 microns), for example less than 40 x 10'6metres (40 microns), optionally less than 20 x 10'6metres (20 microns).. The at least one pump passage may have a minimum cross-sectional extent greater than 0.1 x 10'6metres (1 micron), for example greater than 1 x 10'6metres (1 micron), optionally greater than 4 x 10'6metres (4 microns).

[0082] The at least one pump passage may have a rounded cross-sectional shape, such as a substantially circular cross-sectional shape.

[0083] In accordance with a seventh aspect of the present invention, there is provided a pumping apparatus for pumping a liquid, the pumping apparatus comprising a plurality of pump assemblies as described hereinbefore.

[0084] There may be provided a controller for a pumping apparatus as described hereinbefore.

[0085] Thus, a plurality of volumes of the liquid may be pumped simultaneously, resulting in an even higher throughput of pumped liquid as compared with a single pumpassembly. It may be that the plurality of pump assemblies are together for pumping a plurality of different liquids.

[0086] The plurality of pump assemblies may be at least four pump assemblies. The plurality of pump assemblies may be at least 25 pump assemblies. The plurality of pump assemblies may be at least 100 pump assemblies. The plurality of pump assemblies may be at least 500 pump assemblies. The plurality of pump assemblies may be no more than 250,000 pump assemblies. The plurality of pump assemblies may be no more than 10,000 pump assemblies.

[0087] The plurality of pump assemblies may be arranged such that the pump passages are provided in a grid arrangement.

[0088] Each of the plurality of pump assemblies may share a common substrate. Each of the plurality of pump assemblies may share a common membrane layer. Each of the plurality of pump assemblies may share a common protective layer. Each of the plurality of pump assemblies may comprise a respective piezoelectric actuator. Each of the plurality of pump assemblies may be individually controllable.

[0089] The pumping apparatus may further comprise a power source to power the control circuitry and the piezoelectric actuator or the plurality of piezoelectric actuators. The power source typically comprises an energy storage component, such as a battery.

[0090] The pumping apparatus may further comprise a controller to send one or more control signals to the control circuitry to thereby control pumping of the liquid by the plurality of pump assemblies. The controller may be substantially similar to the controller as described hereinbefore.

[0091] The controller may comprise one or more processors and a memory configured to store instructions which when executed by the one or more processors cause the pump assembly to carry out the functions of the controller described herein. The memory may be non-transitory, computer readable memory. The memory may have the instructions stored thereon. The present invention extends to a non-transitory computer-readable medium (e.g. memory) having the instructions stored thereon to control the pump assembly as described herein. The memory may be solid-statememory. The controller may be provided in a single device. In other examples, the controller may be distributed, having a plurality of processors. A first processor may be separated from a second processor in a distributed manner.

[0092] It may be that the controller is configured to actuate the piezoelectric body by applying an electrical potential gradient to the piezoelectric body in a first direction to cause the piezoelectric body to flex in a first sense and then to apply an electrical potential gradient to the piezoelectric body in the opposite direction to cause it to deform in an opposite second sense.

[0093] The electrical potential gradient is applied by regulating the voltages applied to the first and / or second electrodes. It may be that one electrode remains at ground in which case only the voltage applied to the other electrode need be regulated.

[0094] By applying an electrical potential gradient to the piezoelectric body in a first direction to cause the piezoelectric body to flex in a first sense and then applying an electrical potential gradient to the piezoelectric body in the opposite direction to cause it to deform in an opposite second sense, the piezoelectric actuator may act as a push-pull actuator and readily implement both draw and dispense portions of a pumping cycle.

[0095] It may be that the piezoelectric actuator comprises one or more materials processable at a temperature below 450°C.

[0096] It may be that the piezoelectric actuator comprises a moveable piezoelectric diaphragm comprising the piezoelectric body, the first electrode and the second electrode. It may be that the piezoelectric body comprises one or more piezoelectric materials processable at a temperature below 450°C. Examples of piezoelectric materials that are processable at temperatures below 450°C include aluminium nitride (AIN), zinc oxide (ZnO), and / or scandium aluminium nitride (ScAIN).

[0097] The piezoelectric body may comprise (e.g. be formed from) one piezoelectric material. Alternatively, the piezoelectric body may comprise (e.g. be formed from) more than one piezoelectric material. The piezoelectric body may comprise (e.g. be formed from) a ceramic material comprising aluminium and nitrogen and optionally one or more elements selected from: scandium, yttrium, titanium, magnesium, hafnium, zirconium,tin, chromium, boron. The piezoelectric body may comprise (e.g. be formed from) aluminium nitride (AIN). The piezoelectric body may comprise (e.g. be formed from) zinc oxide (ZnO). The one or more piezoelectric materials may comprise (e.g. consist of) aluminium nitride and / or zinc oxide. Aluminium nitride may consist of pure aluminium nitride. Alternatively, aluminium nitride may comprise one or more elements (i.e. aluminium nitride may comprise aluminium nitride compounds). Aluminium nitride may comprise one or more of the following elements: scandium, yttrium, titanium, magnesium, hafnium, zirconium, tin, chromium, boron. The piezoelectric body may comprise (e.g. be formed from) scandium aluminium nitride (ScAIN).

[0098] Some electronics (e.g., CMOS components) can be damaged at temperatures greater than 450°C. By using piezoelectric materials that are processable at a temperature below 450°C, piezoelectric actuators and electronic components can be integrated whilst avoiding degradation of the electronics, thereby improving the operation and efficiency of the device.

[0099] The piezoelectric actuator may be deposited on (e.g., formed on) the substrate. The piezoelectric actuator may be deposited using one or more PVD methods. Importantly, the piezoelectric actuator is formed on the substrate rather than being formed separately and later bonded.

[0100] The substrate may comprise a silicon wafer. The substrate may be a semiconductor substrate. The controller may be control circuitry comprised within the substrate.

[0101] By providing a pump assembly having integrated control circuitry electrically coupled to the piezoelectric actuator deposited on the substrate, it is possible to provide a highly integrated device having a small-form factor. This arrangement avoids or limits the need for separate electronics (not integrated with the control circuitry). Accordingly, it is made possible to provide pump assemblies which are portable whilst also having the high functionality (e.g., control / sensing) enabled by the combination of a piezoelectric actuator and control circuitry.

[0102] Since each piezoelectric actuator is formed on the substrate having the integrally formed control circuitry, the device is also relatively straightforward to manufacture.The control circuitry may comprise or be an integrated circuit. It may be that the control circuity comprises CMOS control circuitry.

[0103] The CMOS control circuitry may be formed using conventional CMOS fabrication techniques (e.g. ion implantation, chemical vapour deposition (CVD), physical vapour deposition (PVD), etching, chemical-mechanical planarization (CMP) and / or electroplating).

[0104] The at least one pump passage may be through the plurality of layers. Thus, the piezoelectric actuator is on the same surface as defines the at least one pump passage. Thus, particularly efficient pumping of the liquid can be provided.

[0105] In a final aspect, there is provide computer program code or semiconductor fabrication instructions which, when executed by a processor or executed as semiconductor fabrication steps, create a controller as aforesaid.

[0106] Although the embodiments described above (and below) with reference to the drawings may comprise computer-related methods or apparatus, the invention may also extend to program instructions, particularly program instructions on or in a carrier, adapted for carrying out the processes of the invention or for causing a computer to perform as the computer apparatus of the invention. Programs may be in the form of source code, object code, a code intermediate source, such as in partially compiled form, or any other form suitable for use in the implementation of the processes according to the invention. The carrier may be any entity or device capable of carrying the program instructions.

[0107] Thus, there is specifically provided in a further aspect of the invention a non-transitory computer readable medium encoding computer program code which, when executed on at least one processor of a computer, causes the computer (or any appropriate combination of computers, with appropriate distribution of the computer program code) to carry out any appropriate method as aforesaid.

[0108] For example, the carrier may comprise a storage medium, such as a magnetic recording medium, for example a solid state disk or hard disk, or flash memory, optical memory, and so on. Further, the carrier may be a transmissible carrier such as anelectrical or optical signal which may be conveyed via electrical or optical cable or by radio or other means. When a program is embodied in a signal which may be conveyed directly by cable, the carrier may be constituted by such cable or other device or means.

[0109] It will be understood that features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

[0110] Description of the Drawings

[0111] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0112] Figure 1 shows a schematic cross-sectional view of a pump assembly according to an example of the present invention;

[0113] Figures 2(a) and 2(b) show a schematic cross-sectional view of a pump assembly in operation according to an example of the present invention;

[0114] Figure 3 shows a schematic cross-sectional view of a pump assembly according to another example of the present invention;

[0115] Figure 4 shows an example of a typical drive waveform according to the prior art;

[0116] Figure 5 shows three example waveforms of actuation signals in accordance with the present invention;

[0117] Figure 6 shows a pumping apparatus in accordance with another example of the present invention;

[0118] Figures 7(a) and 7(b) show a schematic cross-sectional view of a pump assembly according to another example of the present invention;

[0119] Figure 8 shows a simplified manufacturing process flow for forming a pump assembly in accordance with an example of the present invention;

[0120] Figure 9 shows a system diagram for a pumping apparatus in accordance with another example of the present invention;

[0121] Figure 10 shows a flow chart illustrating steps of a method according to an example of the present invention;Figure 11 shows a flow chart illustrating steps of a method according to an example of the present invention; and

[0122] Figure 12 shows a flow chart illustrating steps of a method according to an example of the present invention.

[0123] Detailed of an Example Embodiment

[0124] Figure 1 shows a schematic cross-sectional view of a pump assembly according to an example of the present invention. The pump assembly 100 comprises a substrate 102 having a first surface 104 and a second surface 106 opposite the first surface 104. The pump assembly further comprises a plurality of layers 108 on the first surface 104 of the substrate 102. The plurality of layers 108 comprises at least a membrane layer 110, a piezoelectric actuator 112 formed on a portion of the membrane layer 110, and a protective layer 114 covering the piezoelectric actuator 112 and the portion of the membrane layer 110 not having the piezoelectric actuator formed thereon, so as to provide an external surface of the pump assembly 100. The piezoelectric actuator 112 is formed of a first electrode 116 formed on the membrane layer 110, a piezoelectric body 118 formed on the first electrode 116, and a second electrode 120 formed on the piezoelectric body 118. Each of the first and second electrodes 116, 120 are in electrical connection with a controller (not shown in Figure 1).

[0125] The pump assembly 100 further comprises a fluid chamber 122, defined at least in part by the substrate 102 and at least in part by the membrane layer 110. The fluid chamber 122 typically extends from the second surface 106 of the substrate 102 to the first surface 104 of the substrate 102. The membrane layer 110 comprises a moveable portion 124 on which, in this example, the piezoelectric actuator 112 is formed. The moveable portion 124 of the membrane layer 110 extends beyond the substrate 102 and across the fluid chamber 122, and so is able to move independently of the substrate 102.

[0126] The pump assembly further comprises a pump passage 126 defined by the plurality of layers 108 and in fluid communication with the fluid chamber 122. The pump passage 126 has an inner portion defined by the moveable portion 124 of the membrane layer 110 and an outer portion defined by the protective layer 114.In use, the fluid chamber 122 is filled with a liquid, and the pump assembly 100 is typically mounted on a substrate that can supply fluid to the fluid chamber 122.

[0127] Figures 2(a) and 2(b) show two schematic cross-sectional views of the pump assembly 100 of Figure 1 in operation with the moveable portion 124 of the membrane layer 110 in a neutral position. In operation, and as shown in Figures 2(a) and 2(b), the pump assembly 100 is provided with a liquid, which is pumped out of the pump assembly 100 from the fluid chamber 122 via the pump passage 126. The form of the liquid as it is pumped out of the pump assembly 100 is affected by the viscosity and surface tension of the liquid. Figures 2(a) and 2(b) show an example of one possible form of the liquid as it is pumped out of the pump assembly 100. In this example, the liquid extends out of the outer portion of the pump passage 126 in a liquid stalk 128. As each subsequent volume of the liquid is pumped out of the pump assembly 100, the liquid within the liquid stalk 128 moves away from the pump passage 126, eventually separating into droplets. The operation of the piezoelectric actuator 112 will be described in more detail with reference to Figure 3, however, it will be understood that the piezoelectric actuator 112 of Figures 2(a) and 2(b) has received an actuation signal comprising a plurality of driving signals, wherein receipt of each driving signal at the piezoelectric actuator 112 causes a volume of the liquid to be pumped from the fluid chamber 122 through the pump passage 126. Figure 2(a) shows a snapshot of first, second, third and fourth volumes 130, 132, 134, 136 of the liquid which have been consecutively pumped from the pump assembly 100, with the first volume 130 having been pumped first (of the four volumes shown) and the fourth volume 136 having been pumped most recently. It will be understood that further volumes of the liquid have been pumped prior to the first volume 130, but that these are not shown in Figures 2(a) and 2(b) for simplicity. Figure 2(b) shows a snapshot of the same first, second, third, and fourth volumes 130, 132, 134, 136 of the liquid after a fifth volume 138 has been pumped from the pump assembly 100.

[0128] In Figure 2(a), the fourth volume 136 forms a proximal bulge in the liquid stalk 128; the third volume 134 forms a distal bulge at the end of the liquid stalk 128; the second volume 132 has just detached from the liquid stalk 128 and the first volume 130 has completely detached and continued to move away from the stalk 128 as a droplet.In this example, each of the first, second, third and fourth volumes 130, 132, 134, 136 continues to move away from the pump assembly 100, and would continue to move away from the pump assembly if the actuation signal were to stop being received at the piezoelectric actuator 112.

[0129] In Figure 2(b), the fifth volume 138 of the liquid is pumped out of the pump assembly and injected into the liquid stalk 128. The fourth volume 136 of the liquid has moved away from the pump assembly, further down the liquid stalk 128. As the third volume 134 of the liquid continues to move away from the pump assembly 100, it overcomes the surface tension of the liquid keeping it attached to the liquid stalk 128, and breaks off into a droplet, taking the place of the second volume 132 of the liquid, which has continued to move away from the pump assembly as a droplet, following the first volume 130 of the liquid which has continued further from the pump assembly.

[0130] This process repeats each time that a driving signal is received at the piezoelectric actuator 112, resulting in a steady stream of droplets being pumped from the pump assembly.

[0131] Figure 3 shows a schematic cross-sectional view of a pump assembly according to another example of the present invention. The pump assembly 200 is substantially similar to the pump assembly 100 shown in Figure 1 and Figures 2(a) and 2(b), apart from the hereinafter noted distinctions unless inherently incompatible therewith. Like features are illustrated with like reference numbers, with the first digit changing from 1 to 2, to indicate that the feature is relevant to Figure 3 instead of Figure 1 and Figure 2(a) and 2(b) (e.g., the membrane layer 110 of Figures 1, 2(a) and 2(b) corresponds to the membrane layer 210 of Figure 3). Specifically, the pump assembly 200 includes a substrate in the form of a silicon substrate 202 having a first surface 204 and a second surface 206, a plurality of layers 208 including a membrane layer 210 with moveable portion 224, piezoelectric actuator 212 and a protective layer 214, a fluid chamber 222 and a pump passage 226. The piezoelectric actuator 212 of Figure 3 extends beyond the extent of the fluid chamber 222 and thus beyond the moveable portion 224 of the membrane layer 210. The piezoelectric actuator 212 is formed of a lower electrode 216 formed on the membrane layer 210, a piezoelectric body 218 formed on the first electrode 216, and an upper electrode 220 formed on the piezoelectric body 218. The piezoelectric body 218 in this example is formed of AIN orScAIN but may be formed of any other suitable piezoelectric material which is processable at a temperature of below 450°C. The piezoelectric actuator 212 forms a diaphragm with layers of materials such as silicon, silicon oxide, silicon nitride or derivatives thereof. The membrane layer 210 functions as a passivation layer which prevents applied electrical potentials from contacting the liquid.

[0132] The substrate 202 comprises a controller in the form of driving circuitry 240 on the first surface 204 of the silicon substrate 202. The driving circuitry 240 is for receiving control signals and generating driving signals to control operation of the piezoelectric actuator 212. The driving circuitry 240 is typically an integrated circuit in the form of a CMOS circuit 240. The person skilled in the art will appreciate that a CMOS circuit comprises both doped regions of the substrate and metallisation layers and interconnections formed on the first surface 206 of the silicon substrate 202. Typically, the CMOS circuit 240 comprises patterned regions of doped silicon and metallisation layers. The number of metallisation layers depends on the complexity of the CMOS control circuit, but three layers should suffice for many applications.

[0133] The membrane layer 210 defines a wall of the fluid chamber 222 which receives liquid through a fluid chamber inlet 223. The fluid chamber 222 is in fluid communication with the pump passage 226 for ejecting the liquid. The protective layer 214 and the membrane layer 210 define a wall of the pump passage 226. The fluid chamber inlet 223 forms at least part of a liquid manifold providing a liquid communication pathway between a supply cavity (not shown in Figure 3) and the pump passage 226 (as well as, in some examples, further pump passages, not shown in Figure 3), via the fluid chamber 222. The fluid chamber inlet 223 is defined by the silicon substrate 202. The protective layer 214 is provided to cover and protect the piezoelectric actuator 212, and abuts against a surface 210A of the membrane layer 210. The protective layer 214 has an aperture which defines the pump passage 226.

[0134] The pump assembly of Figure 3 pumps liquid through the pump passage 226. The piezoelectric actuator 212 is formed on the membrane layer 210 which moves with the pump passage 226. Thus, the surface of the fluid chamber 222 that includes the pump passage 226, i.e., the surface defined by the membrane layer 210, is the surface that moves during actuation. This contrasts with devices in which the surface that includes the pump passage does not move and another surface, e.g., the opposite surface, isactuated. As a result, only a relatively small actuation force is required to displace the liquid in the pump passage. The liquid is then pumped mainly by inertial force (i.e. inertial ejection) from the pump passage. Herein, ejection by inertial force can also be referred to as inertial ejection or ejection by inertial mode. The ejection of the liquid is dictated predominantly by the density and viscosity of the liquid - not by compressibility as would be the case if another surface was actuated and the liquid in the chamber was displaced as a whole in order to cause the ejection.

[0135] In use, the pump assembly 200 is mounted on a support including a liquid manifold that supplies liquid to the fluid chamber 222 via the fluid chamber inlet 223. The action of pumping of the liquid typically causes the liquid to be drawn towards the pump passage 226, causing the fluid chamber 222 to continually be replenished with liquid via the fluid chamber inlet 223. The action of pumping the liquid typically results in a liquid stalk (illustrated in Figure 2(b)), wherein the momentum of the liquid in the liquid stalk prevents the liquid from being drawn back into the pump passage 226 during a subsequent pumping cycle. In the absence of actuation of the piezoelectric actuator 212, the liquid does not move onto the outer surface of the protective layer 214 past the pump passage 226 due to at least one of surface tension, negative fluid pressure of the liquid relative to the region outside the outer surface of the protective layer 214, and the geometry of the pump passage 226.

[0136] Although only one pump passage 226, fluid chamber 222, and piezoelectric actuator 212 is shown in Figure 3 for clarity, it will be understood that a plurality of pump passages and corresponding fluid chambers and piezoelectric actuators are typically provided together as a plurality of pump assemblies on the same substrate 202. Each piezoelectric actuator 212 is configured to control pumping of the liquid from the respective pump passage 226. For completeness, it is also noted that there may be a plurality of pump passages per piezoelectric actuator 212.

[0137] The driving circuitry 240 has first, second, and third portions 240A, 240B, 240C. The first portion 240A of the driving circuitry 240 is in electrical communication with a bond pad 242 via first electrical interconnects 244A such that signals from an external controller (not shown) may be conducted to the first portion 240A of the driving circuitry 240 via the bond pad 242. The second portion 240B of the driving circuitry 240 is in electrical communication with the upper electrode 220 via second electricalinterconnect 244B and the third portion 240C of the driving circuitry 240 is in electrical communication with the lower electrode 216 via third electrical interconnect 244C so that signals from the external controller may be conducted from the second and third portions 240B, 240C of the driving circuitry 240 to the upper and lower electrodes 220, 216, which are arranged to apply an electric potential difference across and thereby actuate the piezoelectric body 218. An opening is defined in the piezoelectric body 218 for passage of the third electrical interconnect 244C between the third portion 240C of the driving circuitry 240 and the upper electrode 220.

[0138] The second and third portions 240B, 240C of the driving circuitry 240 control the application of a driving signal in the form of a voltage pulse to the lower and upper electrodes 216, 220 according to a signal from the first portion 240A of the driving circuitry 240. The application of electrode voltage across the piezoelectric body 218 creates an electric field. The application of this field causes a deformation of the piezoelectric body 218. The deformation can either be tensile or compressive strain depending on the orientation of the electric field with respect to the direction of polarisation in the material. The induced strain caused by the expansion of contraction of the piezoelectric body 218 induces a strain gradient through the thickness of the moveable portion 224 of the membrane layer 210, piezoelectric actuator 212 and the protective layer 214 causing a movement or displacement in a direction parallel to an axis defined by the pump passage 226. The mechanical properties of the protective layer 214 are chosen to minimise the effect of the forcing action of the piezoelectric actuator 212. The protective layer 214 is thus more resistant to being moved by the expansion and contraction of the piezoelectric body than the membrane layer 210.

[0139] The piezoelectric properties of the piezoelectric material can be characterized in part by the transverse piezoelectric constant d31. d31is the particular component of the piezoelectric coefficient tensor which relates the electric field applied across the piezoelectric material in a first direction to the strain induced in the piezoelectric material along a second direction perpendicular to said first direction. The piezoelectric actuator 212 shown is configured such that the applied electric field induces a strain in the material in a direction perpendicular to the direction in which the field is applied and is therefore characterized by the d31constant.The application of a DC or constant electric field can cause a net positive or net negative displacement of the moveable portion 224, depending on the direction of the electric field.

[0140] The application of a pulsed electric field can cause an oscillation of the moveable portion 224. An electric field pulse will either result in a positive or a negative displacement of the moveable portion 224, depending on the direction of the electric field of the pulse. A positive displacement will occur when the electric field pulse applied across the electrodes causes an extension in the piezoelectric body 218. This causes a deflection of the moveable portion 224 away from the fluid chamber 222, which introduces a negative fluid pressure under the moveable portion 224, causing the liquid to move towards the pump passage. A negative displacement occurs when a reverse field pulse is applied, i.e. , an electric field pulse which, when applied across the electrodes, causes a contraction in the piezoelectric body 218. This causes a deflection of the moveable portion 224 towards and into the space of the fluid chamber 222, introducing a positive pressure in the fluid chamber and thus causing liquid to be pumped through the pump passage and out of the pump assembly. By timing the application of the electric field pulses, a pulsed electric field can be applied to the piezoelectric actuator 212, causing an oscillation of the moveable portion 224. The frequency and amplitude of the oscillation of the moveable portion 224 is primarily a function of the mass and stiffness characteristics of the membrane layer 210, piezoelectric actuator 212 and protective layer 214, the properties of the liquid (e.g., liquid density, liquid viscosity and surface tension), the geometries of the pump passage 226 and fluid chamber 222 and the configuration of the driving signals.

[0141] Figure 4 shows an example of a driving signal 350 used to operate a typical droplet-on-demand droplet ejector according to the prior art. A first pulse 352 will cause an oscillation of the moveable portion to pump a first droplet of fluid. However, in these systems it is necessary to have a settling time 354 before a second pulse 356 can be sent to pump a second droplet of fluid. The settling time 354 is necessary in order for the moveable portion to stop oscillating and for the pump passage to prime with the liquid. The first pulse 352 and the second pulse 356 are each a single voltage pulse of alternating current in which the voltage increases from zero to a positive peak, then decreases to a negative trough before returning to zero. In this example, the first andsecond pulses 353, 356 each have a period of oscillation aligned with the oscillation of the moveable portion of the membrane layer.

[0142] Figure 5 shows examples of possible waveforms of actuation signals for use in driving a piezoelectric actuator as described hereinbefore. The x-axis for each of the three examples is in time (in microseconds, ps), and the y-axis is the amplitude of the actuation signal (in volts, V). First, second and third actuation signals 360, 362, 364 are shown in Figure 5.

[0143] The first actuation signal 360 can be considered to be comprised of a plurality of driving pulses, each of which causes a volume of the fluid to be pumped, and wherein each pulse is substantially similar to the first and second pulses 352, 356 of Figure 4. The settling time 354 associated with the typical drive waveform in Figure 4 is shown in Figure 5 for comparison. The first actuation signal 360 is substantially sinusoidal, alternating between a peak positive voltage and a peak negative voltage, both of equal magnitude. The frequency of the first actuation signal 360 is aligned with the oscillation frequency of the moveable portion of the membrane. Thus, the receipt of the first actuation signal 360 at the piezoelectric actuator will cause the moveable portion to oscillate at resonance. In this way, a first driving pulse will induce an oscillation of the membrane, and the following pulse will reinforce that movement, causing it to continue to smoothly oscillate in the same direction as it would have continued to oscillate. Thus, a greater volume of fluid can be pumped in the same amount of time, as there is no need to wait for the membrane to come to rest, and it is more energy efficient as the energy used to cause an oscillation is not then wasted by allowing the membrane to come to rest.

[0144] The second example actuation signal 362 is substantially similar in effect to the first actuation signal, but with more of a square waveform. The periodicity of the second actuation signal 362 is aligned with the oscillation frequency of the moveable portion.

[0145] The third example actuation signal 364 begins similarly to the second actuation signal 362, but every other positive peak is replaced with a held negative voltage. This acts to dampen the oscillation of the moveable portion after the first volume of the liquid is pumped. This is useful in applications where it is still necessary for the membrane tocome substantially to rest between each droplet ejection, and still creates a higher throughput than the typical waveform of Figure 4.

[0146] Figure 6 shows a schematic of a top-down view of an example of a pumping chip in accordance with an aspect of the present invention. The pumping chip 670 comprises a substrate in the form of a silicon substrate 672 with first, second and third pluralities of pump assemblies 674, 676, 678 situated thereon. Each of the first, second and third plurality of pump assemblies 674, 676, 678 are presented in a grid-like arrangement. The pumping chip 670 further comprises a plurality of bond pads 680 which are in electrical communication with the pump assemblies for sending driving signals thereto. The plurality of bond pads 680 are in further electrical communication with a controller (not shown in Figure 6) for receiving driving signals therefrom. Each of the pump assemblies may be substantially similar to the pump assembly of Figures 1 and 2.

[0147] Typically, for the pumping chip 670 of Figure 6, a first set 680A of the plurality of bond pads 680 are in electrical communication with the first plurality of pump assemblies 674, a second set 680B of the plurality of bond pads 680 are in electrical communication with the second plurality of pump assemblies 676, and a third set 680C of the plurality of bond pads 680 are in electrical communication with the third plurality of pump assemblies 678. The first plurality of pump assemblies 674 is thus configured to be capable of being operated in both a droplet-on-demand mode and a continuous mode, while the second and third pluralities of pump assemblies 676, 678 operate solely in a continuous mode, thus reducing manufacturing cost and the complexity of the chip. In this way, a controllable range of pumped volume rates can be achieved using a single chip depending on the operating regime chosen.

[0148] Figures 7(a) and 7(b) show a schematic cross-sectional view of a pump assembly according to another example of the present invention. The pump assembly 700 is shown unfilled in Figure 7(a) and is shown filled with liquid and in operation in Figure 7(b), substantially similar to the depictions of the pump assembly 100 shown in Figure 1 and Figure 2, respectively. The pump assembly 700 shown in Figure 7(a) and in operation in Figure 7(b) is substantially similar to the pump assembly 100 shown in Figure 1 and shown in operation in Figure 2, apart from the hereinafter noted distinctions unless inherently incompatible therewith. Like features are illustrated with like reference numbers, with the first digit changing from 1 to 7, to indicate that thefeature is relevant to Figures 7(a) and 7(b) instead of Figures 1 and 2 (e.g., the membrane layer 110 of Figures 1 and 2 corresponds to the membrane layer 710 of Figures 7(a) and 7(b)). Specifically, the pump assembly 700 includes a substrate 702 having a first surface 704 and a second surface 706, a plurality of layers 708 including a membrane layer 710 with moveable portion (not labelled in Figures 7(a) and 7(b)), piezoelectric actuator 712 and a protective layer 714.

[0149] The pump assembly 700 further comprises a fluid chamber 722 in fluid communication with a first pump passage 777 and with a second pump passage 779. Each of the first and second pump passages 777, 779 are defined by the plurality of layers 708 and extend through the piezoelectric actuator 712, an inner diameter of which is larger in comparison to an inner diameter of the piezoelectric actuator 112 of Figures 1, 2(a) and 2(b) so as to accommodate both of the first and second pump passages 777, 779.

[0150] The operation of the pump assembly 700 is substantially similar to the operation of pump assembly 100. The pump assembly 700 is shown in operation in Figure 7(b). The movement of the moveable portion in response to receipt of a driving signal at the piezoelectric actuator 712 causes liquid to be pumped through both of the first and second pump passages, forming two distinct liquid stalks 728A, 728B from which first and second sets of droplets 781 A, 781 B are released. Each droplet in the first set of droplets is released simultaneously to a droplet in the second set of droplets 781 B. In this example, each of the droplets has the same volume, which is predetermined.

[0151] Figure 8 illustrates stages in a simplified manufacturing process flow for forming a pump assembly in accordance with examples described herein. The droplet ejector 400 is substantially similar to the droplet ejector 200 shown in Figure 3, apart from the hereinafter described differences. Like features are illustrated with like reference numbers, with the first digit changing from 3 to 4, to indicate that the feature is relevant to Figure 8 instead of Figure 3 (e.g., the membrane layer 210 of Figure 3 is the membrane layer 410 of Figure 8). Specifically, the pump assembly 400 includes a substrate 402, a membrane layer 410, piezoelectric actuator 412, protective layer 414, fluid chamber 422, pump passage 426, bond pad 442, and first and second portions 440A, 440B, 440C of driving circuitry 440.A first manufacturing step, as shown in Figure 8(a), is to create the driving circuitry 440 and a plurality of layers shown generally as an interconnect layer 433, for example CMOS driving circuitry 440 and interconnects 433, on a surface of a silicon substrate 440. The interconnect layer 433 is typically a CMOS metallisation layer and comprises metal conductive traces and a passivation insulator such as SiO2, SiN, SiON. The CMOS driving circuitry 440 is formed by standard processes - for example ion implantation on p-type or n-type substrates followed by the creation of a wiring interconnect layer by standard CMOS fabrication processes (e.g. ion implantation, chemical vapour deposition (CVD), physical vapour deposition (PVD), etching, chemical-mechanical planarization (CMP) and / or electroplating).

[0152] Subsequent manufacturing steps are implemented to define features and structures of the pump assembly. Subsequent steps are chosen not to damage structures formed in previous steps. A key manufacturing parameter is the peak processing temperature. Problems associated with processing CMOS at high temperatures include the degradation of dopant mobility and interconnect wiring schemes. CMOS electronics are known to survive temperatures of 450°C. However, a much lower temperature (i.e. below 300°C) is desirable for high yield.

[0153] The membrane layer 410, piezoelectric actuator 412, protective layer 414 and bond pad 442 are formed on top of the interconnect layer 433 as shown in Figure 8(b). The membrane layer 410 is deposited using a CVD or PVD process.

[0154] The formation of a CMOS compatible piezoelectric material within the piezoelectric actuator 412 is of particular interest as this is the key driving element of the piezoelectric actuator 412.

[0155] ZnO, AIN and AIN compounds (such as ScAIN) materials can be deposited using low-temperature PVD (e.g. sputtering) processes that do not require post processing such as annealing. These materials also do not require poling.

[0156] ZnO, AIN and AIN compounds (e.g. ScAIN) materials are therefore commercially viable materials for the fabrication of a monolithic pump assembly. However, the value of d31for these materials is significantly lower than that of PZT. The particular configuration of the moveable portion of the membrane layer 410, which improves ejection efficiency,and the use of two control electrodes, which improves actuation efficiency, counter the lower d31value associated with these materials.

[0157] Piezoelectric electrode materials are deposited using a CMOS compatible process such as PVD (including low-temperature sputtering). Typical electrode materials may include titanium (Ti), platinum (Pt), aluminium (Al), tungsten (W) or alloys thereof. The electrodes of the piezoelectric actuator 412 are defined by standard patterning and etch methods.

[0158] Protective materials can be deposited and patterned using a spin on and cure method (suitable for polyimides or other polymeric materials). Some materials, such as PTFE, may require more specific deposition and patterning approaches.

[0159] Bond pads are deposited using methods such as CVD or PVD (e.g. sputtering).

[0160] The fluid chamber is defined using high aspect ratio Deep Reactive Ion Etching (DRIE) methodologies to arrive at the shape shown in Figure 8(c). The fluid chamber is aligned to the pump passage using a wafer front-back side alignment tool. The wafer may be mounted on a handle wafer during the front-back alignment and etch steps.

[0161] Figure 9 shows a system diagram for a pump apparatus according to an example of the present invention. The pump apparatus 901 comprises a plurality of components, including a plurality of actuator portions 910, and a controller 920. The controller 920 is configured to exchange signals 915 with the plurality of actuator portions 910 to control the plurality of actuator portions 910 in accordance with input signals received by the controller 920. The controller 920 in this example is realised by one or more processors 930 and a computer-readable memory 940. The memory 940 stores instructions which, when executed by the one or more processors 930, cause the pump apparatus 901 to operate as described herein.

[0162] Figure 10 shows a flow chart illustrating steps of a method according to an example of the present invention. The method 1000 is a method of pumping a liquid. Specifically, the method 1000 comprises providing 1010 a pump assembly. The pump assembly is substantially as described in any of the examples hereinbefore. The method 1000 further comprises receiving 1020 a first driving signal at the piezoelectric actuator,causing movement of the moveable portion, and, in response, causing 1030 a first volume of the liquid to be pumped via the at least one pump passage. The method 1000 further comprises receiving 1040 a second driving signal at the piezoelectric actuator while the moveable portion is still moving, causing movement of the moveable portion, and, in response, causing 1050 a second volume of the liquid to be pumped via the at least one pump. More than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the time at which the second driving signal is received at the piezoelectric actuator, would be in the same direction as would be caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.

[0163] Figure 11 shows a flow chart illustrating steps of a method according to another example of the present invention. The method 1100 is a method of pumping a liquid. Specifically, the method 1100 comprises providing 1110 a pump assembly. The pump assembly is substantially as described in any of the examples hereinbefore. The method 1100 further comprises receiving 1120 a first driving signal at the piezoelectric actuator, causing movement of the moveable portion, and, in response, causing 1130 a first volume of the liquid to be pumped via the at least one pump passage. The method 1100 further comprises receiving 1140 a second driving signal at the piezoelectric actuator while the moveable portion is still moving, causing movement of the moveable portion, and, in response, causing 1150 a second volume of the liquid to be pumped via the at least one pump passage, wherein the second volume of the liquid is predetermined.

[0164] Figure 12 shows a flow chart illustrating steps of a method according to another example of the present invention. The method 1200 is a method of pumping a liquid. Specifically, the method 1200 comprises providing 1210 a pump assembly. The pump assembly is substantially as described in any of the examples hereinbefore. The method 1200 further comprises receiving 1220 a first driving signal at the piezoelectric actuator causing movement of the moveable portion, and, in response, causing 1230 a first volume of the liquid to be pumped via the at least one pump passage. The first driving signal comprises a first region up to an escape point at which the first volume of the liquid is moving away from the at least one pump passage with sufficient momentum to continue progressing away from the pump assembly in the absence ofany further driving signal. The method 1200 further comprises receiving 1240 a second driving signal at the piezoelectric actuator within a settling time of the first driving signal, causing movement of the moveable portion, wherein the settling time of the first driving signal is the time it would take for the moveable portion to naturally come to rest after movement caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator, and, in response, causing 1250 a second volume of the liquid to be pumped via the at least one pump passage, wherein the second volume of the liquid is predetermined.

[0165] In each of the methods 1000, 1100, 1200 described with reference to Figures 10, 11 and 12, respectively, the first and second volumes of the liquid are caused to be pumped by receipt of the driving waveforms described hereinabove (or another driving waveform) at the piezoelectric actuator.

[0166] In summary, there is provided a method of pumping a liquid, the method comprising providing a pump assembly (100, 200, 400, 700). The pump assembly comprises: a substrate (102, 202, 402, 702) having a first surface (104, 204, 704) and an opposite second surface (106, 206, 706) the substrate comprising control circuitry (240, 440); a plurality of layers (108, 208, 708) on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator (112, 212, 412, 712) providing a piezoelectric body (118, 218) and a first electrode (116, 216) and a second electrode (120, 220) in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the control circuitry, and wherein the plurality of layers comprises a moveable portion (124, 224); and at least one pump passage (126, 226, 426, 777, 779) defined by the pump assembly. The method further comprises causing a first volume of the liquid to be pumped via the at least one pump passage in response to receipt of a first driving signal at the piezoelectric actuator causing movement of the moveable portion; and causing a second volume of the liquid to be pumped via the at least one pump passage in response to receipt of a second driving signal at the piezoelectric actuator causing movement of the moveable portion. In this aspect, the second driving signal is received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator, and more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the time at which the second driving signal is received at thepiezoelectric actuator, would be in the same direction as would be caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.

[0167] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to and do not exclude other components, integers, or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0168] Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

42Claims1. A method of pumping a liquid, the method comprising:providing a pump assembly comprising:a substrate having a first surface and an opposite second surface; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to a controller, and wherein the plurality of layers comprises a moveable portion; andat least one pump passage defined by the pump assembly; causing a first volume of the liquid to be pumped via the at least one pump passage in response to receipt of a first driving signal at the piezoelectric actuator causing movement of the moveable portion; andcausing a second volume of the liquid to be pumped via the at least one pump passage in response to receipt of a second driving signal at the piezoelectric actuator causing movement of the moveable portion,wherein the second driving signal is received at the piezoelectric actuator whilst the moveable portion is still moving as a result of receipt of the first driving signal at the piezoelectric actuator, and more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the time at which the second driving signal is received at the piezoelectric actuator, would be in the same direction as would be caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.

2. A controller for a pump assembly, the pump assembly comprising:a substrate having a first surface and an opposite second surface;a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; andat least one pump passage defined by the pump assembly,wherein the controller is configured to:cause a first driving signal to be received at the piezoelectric actuator at a first time; and43cause a second driving signal to be received at the piezoelectric actuator at a second time, after the first time,wherein the piezoelectric actuator is configured to:cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage; andcause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage, wherein the time between the first time and the second time is less than the time from the first time in which the moveable portion would naturally come to rest after the movement caused in response to receipt of the first driving signal at the piezoelectric actuator, and more than 50% of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, after the second time, would be in the same direction as the movement of the moveable portion caused in response to receipt of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary at the second time.

3. The method of claim 1 or the controller of claim 2, wherein either the second driving signal is received at the piezoelectric actuator, or the controller is configured to cause the second driving signal to be received at the piezoelectric actuator, when the moveable portion is moving in response to receipt of the first driving signal at the piezoelectric actuator in the same direction as movement of the moveable portion which would be caused in response to receipt of an initial portion of the second driving signal at the piezoelectric actuator were the moveable portion to be stationary when the second driving signal is received at the piezoelectric actuator.

4. The method or the controller of any preceding claim, wherein either:the difference in time between the time of receipt of the first driving signal at the piezoelectric actuator and the time of receipt of the second driving signal at the piezoelectric actuator is within half of a period of oscillation of the moveable portion of a multiple of the period of oscillation of the moveable portion; orthe difference between the first time and the second time is within half of a period of oscillation of the moveable portion of a multiple of the period of oscillation of the moveable portion.

445. A method of pumping a liquid, the method comprising:providing a pump assembly comprising:a substrate having a first surface and an opposite second surface; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to a controller, and wherein the plurality of layers comprises a moveable portion; andat least one pump passage defined by the pump assembly, causing a first volume of the liquid to be pumped via the at least one pump passage in response to receipt of a first driving signal at the piezoelectric actuator causing movement of the moveable portion; andcausing a second volume of the liquid to be pumped via the at least one pump passage in response to receipt of a second driving signal at the piezoelectric actuator causing movement of the moveable portion,wherein the second driving signal is received at the piezoelectric actuator whilst the moveable portion is still moving, as a result of receipt of the first driving signal at the piezoelectric actuator, with an amplitude greater than 5% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, and wherein the second volume of the liquid is predetermined.

6. A controller for a pump assembly, the pump assembly comprising:a substrate having a first surface and an opposite second surface;a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; andat least one pump passage defined by the pump assembly,wherein the controller is configured to:cause a first driving signal to be received at the piezoelectric actuator at a first time; andcause a second driving signal to be received at the piezoelectric actuator at a second time, after the first time,wherein the piezoelectric actuator is configured to:cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage; andcause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage, wherein the time between the first time and the second time is less than the time from the first time in which the amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator would naturally fall to below 5% of the maximum amplitude of the movement of the moveable portion caused in response to receipt of the first driving signal at the piezoelectric actuator, andwherein the second volume of the liquid is predetermined.

7. The method or the controller of any preceding claim, wherein the first driving signal comprises a first region up to an escape point at which the first volume of the liquid is moving away from the at least one pump passage with sufficient momentum to continue progressing away from the pump assembly in the absence of any further driving signal, andwherein the second driving signal is received or the controller causes the second driving signal to be received at the piezoelectric actuator within a settling time of the escape point of the first driving signal, wherein the settling time of the first driving signal is the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 5% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator, andwherein the second volume of the liquid is predetermined.

8. A method of pumping a liquid, the method comprising:providing a pump assembly comprising:a substrate having a first surface and an opposite second surface; a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least oneof the first and second electrodes being electrically connected to a controller, and wherein the plurality of layers comprises a moveable portion; andat least one pump passage defined by the pump assembly, causing a first volume of the liquid to be pumped via the at least one pump passage in response to receipt of a first driving signal at the piezoelectric actuator causing movement of the moveable portion; andcausing a second volume of the liquid to be pumped via the at least one pump passage in response to receipt of a second driving signal at the piezoelectric actuator causing movement of the moveable portion,wherein the first driving signal comprises a first region up to an escape point at which the first volume of the liquid is moving away from the at least one pump passage with sufficient momentum to continue progressing away from the pump assembly in the absence of any further driving signal, andwherein the second driving signal is received at the piezoelectric actuator within a settling time of the escape point of the first driving signal, wherein the settling time of the first driving signal is the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 5% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator, and wherein the second volume of the liquid is predetermined.

9. A controller for a pump assembly, the pump assembly comprising:a substrate having a first surface and an opposite second surface;a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller, and wherein the plurality of layers comprises a moveable portion; andat least one pump passage defined by the pump assembly,wherein the controller is configured to:cause a first driving signal to be received at the piezoelectric actuator at a first time; andcause a second driving signal to be received at the piezoelectric actuator at a second time, after the first time,47wherein the piezoelectric actuator is configured to:cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage; andcause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage, wherein the first driving signal comprises a first region up to an escape point at which the first volume of the liquid is moving away from the at least one pump passage with sufficient momentum to continue progressing away from the pump assembly in the absence of any further driving signal, andwherein the controller causes the second driving signal to be received at the piezoelectric actuator within a settling time of the escape point of the first driving signal, wherein the settling time of the first driving signal is the time it would take for the amplitude of movement of the moveable portion which would be caused in response to receipt of a driving signal made up of the first region of the first driving signal at the piezoelectric actuator to naturally fall to below 5% of a maximum amplitude of the movement of the moveable portion which would be caused in response to receipt of the driving signal made up of the first region of the first driving signal at the piezoelectric actuator, andwherein the second volume of the liquid is predetermined.

10. The method or the controller of any preceding claim, wherein the first volume of the liquid is predetermined, and / or wherein the first volume of the liquid has an equal volume to the second volume of the liquid.

11. The method or the controller of any preceding claim, wherein the first driving signal and the second driving signal are amongst a plurality of consecutive driving signals comprised within an actuation signal, and wherein the actuation signal is received or the controller causes the actuation signal to be received at the piezoelectric actuator in response to receipt of an activation signal indicative of a demand to pump the liquid via the at least one pump passage, optionally wherein the liquid is caused to be pumped via the at least one pump passage in response to receipt of the actuation signal at the piezoelectric actuator, and / or wherein receipt of each of the plurality of consecutive driving signals of the actuation signal at the piezoelectric actuator is48sufficient to cause pumping of the liquid via the at least one pump passage in a respective volume of the liquid, together forming a plurality of volumes of the liquid.

12. The method or the controller of claim 11, wherein each of the plurality of volumes of the liquid have a predetermined volume, and / or wherein at least 50% of the plurality of volumes of the liquid have equal volume.

13. The method or the controller of any preceding claim, wherein causing each of the first volume and the second volume of the liquid to be pumped via the at least one pump passage causes a respective droplet of the liquid to be formed.

14. A pump assembly for pumping a liquid, the pump assembly comprising:a substrate having a first surface and an opposite second surface;a plurality of layers on the first surface of the substrate, the plurality of layers comprising a piezoelectric actuator providing a piezoelectric body and first and second electrodes in contact with the piezoelectric body, at least one of the first and second electrodes being electrically connected to the controller as claimed in any of claims 2, 6 and 9, or any of claims 3 to 5, 7, 8 or 10 to 13 when dependent directly or indirectly thereon, and wherein the plurality of layers comprises a moveable portion;the controller, configured to control the piezoelectric actuator; andat least one pump passage defined by the pump assembly,wherein the piezoelectric actuator is configured to:cause movement of the moveable portion in response to receipt of the first driving signal at the piezoelectric actuator to thereby cause a first volume of the liquid to be pumped via the at least one pump passage; andcause movement of the moveable portion in response to receipt of the second driving signal at the piezoelectric actuator to thereby cause a second volume of the liquid to be pumped via the at least one pump passage.

15. A pumping apparatus for pumping a liquid, the pumping apparatus comprising a plurality of pump assemblies, wherein each pump assembly of the plurality of pump assemblies is the pump assembly as claimed in claim 14.

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