WO2022243666A1

WO2022243666A1 - Electrical component for a microelectromechanical systems device

Info

Publication number: WO2022243666A1
Application number: PCT/GB2022/051232
Authority: WO
Inventors: Andrew VELLA
Original assignee: Xaar Technology Limited
Priority date: 2021-05-17
Filing date: 2022-05-17
Publication date: 2022-11-24
Also published as: GB202106999D0; GB2606721A

Abstract

An electrical component for a microelectromechanical systems device, the electrical component comprising: i) a substrate comprising a first substrate surface and an opposing second substrate surface spaced apart in a thickness direction perpendicular to the first substrate surface; ii) a plurality of electrical elements arranged over the first substrate surface in rows, each row extending in a row direction, wherein each electrical element comprises: a) a first electrode disposed adjacent to the first substrate surface, b) a ceramic member having a first surface disposed in contact with the first electrode and a second surface opposite the first surface, the ceramic member extending in a length direction that is parallel to the first substrate surface and non-parallel to the row direction, and a width direction parallel to the first substrate surface and perpendicular to the length direction; c) a second electrode disposed in contact with the second surface of the ceramic member such that a potential difference may be established between the first and second electrodes and through the ceramic member during operation of the component; d) a passivation layer provided, at least in part, on the second electrode and having vias extending through to the second electrode at opposite ends of the second electrode in the length direction; e) a first electrical trace connecting the first electrode to an external circuit and a second electrical trace connecting the second electrode to the external circuit, wherein each second electrical trace is arranged, at least in part, overlying the respective second electrode and on the passivation layer and each second electrical trace comprises a connecting portion and two electrode connecting points for the respective second electrode, wherein each connecting portion extends in the length direction and is connected to the respective second electrode by said connecting points through said vias of said passivation layer. A microelectromechanical systems device comprising the electrical component. A droplet ejection head comprising the electrical component. A droplet ejection apparatus comprising a droplet ejection head. A method of providing electrical traces to an electrical component for a microelectromechanical systems device.

Description

ELECTRICAL COMPONENT FOR A MICROELECTROMECHANICAL SYSTEMS DEVICE

FIELD OF THE INVENTION

The present invention relates to the field of microelectromechanical systems (MEMS) and, in particular, to an electrical component for a MEMS device, which could, for example, be employed as an electromechanical actuator. It may find particularly beneficial application, as an actuator element, for a droplet deposition or droplet ejection head. A method of manufacture of the electrical elements, included in the component, is also disclosed. The electrical component may be particularly beneficial in applications where a high level of packing of the electrical elements is required.

BACKGROUND

Droplet ejection heads are now in widespread usage, whether in more traditional applications, such as inkjet printing, or in 3D printing, or other materials deposition or rapid prototyping techniques. Accordingly, fluids used in droplet ejection heads often require novel chemical properties to adhere to new substrates and increase the functionality of the deposited material.

A variety of fluids may be deposited by a droplet ejection head. For instance, a droplet ejection head may eject droplets of fluid that travel towards a receiving medium, such as paper or card, ceramic tiles or shaped articles (e.g. cans, bottles etc.) to form an image. Alternatively droplets of fluid may be used to build structures, for example, electrically active fluids may be deposited onto receiving media, such as a circuit board, to enable prototyping of electrical devices, or to deposit droplets of solution containing biological or chemical material onto a receiving medium, such as a microarray of assay tubes. Droplet ejection heads may also be used in applications without a receiving medium. For example, a fine vapour or mist may be generated by droplet ejection heads to control humidity in greenhouse misting systems.

So as to be suitable for new and/or increasingly challenging ejection and deposition applications, droplet ejection heads continue to evolve and specialise. However, while a great many developments have been made, there remains room for improvement. Specifically, increasingly challenging specifications for droplet ejection heads often require improvements in their structure and manufacturing techniques. Electrical elements for MEMS devices, which may serve as electromechanical actuators to drive such droplet ejection heads, are commonly manufactured by depositing a series of layers onto a first substrate, for example, by employing one or more techniques known in the thin film technology field. A typical electrical element may have a configuration where a ceramic member is interposed between two electrically conductive layers, which form a first and a second electrode. The ceramic member may, for example, be a thin film of a ceramic material showing ferroelectric behaviour, such as a piezoelectric material or a relaxor/ferroelectric crossover material. Commonly employed ceramic materials include lead based ceramics with perovskite structure, especially lead titanate zirconate (PZT), doped PZT and PZT-based solid solutions. They may be deposited onto the first substrate through a number of deposition techniques known in the art, for example through sputtering, chemical vapour deposition (CVD) or chemical solution deposition (CSD).

In recent years, significant effort has been put into the development of lead-free alternative materials such as (K,Na)Nb0₃ -based materials, (Ba,Ca)(Zr,Ti)0₃-based materials and (Bi,Na,K)TiC>3-based materials with similar deposition techniques.

Electrical elements formed from such materials are deposited layer by layer on the first substrate, commonly a wafer capable of accommodating several arrays of electrical elements, where the first and second electrodes may be described as forming a lower electrode supporting the thin film of piezoelectric or relaxor/ferroelectric crossover material, and a top electrode covering the thin film material.

The lower electrode may be a common electrode or it may be patterned to form arrays of individual electrodes, each associated with an individual electrical element, whilst the thin film material, similarly, may or may not be patterned. Individual electrical elements, therefore, might comprise a patterned ceramic material thin film or a region of an unpatterned ceramic material thin film common to more than one electrical element. Individually addressable regions of electrical elements may be defined by at least one of the electrodes of each element being patterned.

In other cases, an electrical element may have an electrode configuration in which both first and second electrodes are provided on one surface of the ceramic thin film, for example, as an adjacent or interdigitated pair. This electrode arrangement has the advantage of providing an easier way of connecting the electrodes since they are formed on the same surface, thus simplifying the manufacture of the electrical component. This electrode arrangement is particularly useful for some applications, for example transducers/sensors.

The electrical connection of each electrical element to the drive circuitry may be ensured using electrical traces, generally made of metal or metal alloys, which are directly connected to the electrodes of the electrical element.

One or more insulating or passivating layers are also deposited at various stages of the formation of an electrical element in order to ensure electrical insulation of the electrodes and traces. The passivating layers also protect the various features of the electrical element from chemical attacks caused by the external environment or by chemicals, used either in the production process or during the electrical element operation.

A second substrate, such as a protective layer, for example a capping layer, is usually bonded to the first substrate in order to protect the electrical elements from the external environment, especially moisture and other chemical species. The second substrate may have a recess to accommodate one or more electrical elements.

Usually, a plurality of electrical elements are formed on a surface of a substrate at the same time. The plurality of electrical elements is usually arranged in an array.

The demand for devices capable of ever higher performance, for example, higher resolution and/or higher miniaturisation of devices, requires the electrical elements to be arranged at increasingly high densities.

Some arrangements of the electrical elements on the substrate layer are complicated by the fact that electrical traces are formed on the substrate layer in the regions between adjacent electrical elements. Those features take up space on the surface of the substrate layer and, if a high density of electrical elements has to be achieved, the width of the electrical elements has to be reduced, accordingly.

After the electrical elements have been formed, cavities may be provided underneath the electrical elements by etching the substrate layer from a side opposite the side on which the electrical elements are formed. In the context of a droplet ejection head, these cavities will form the fluid chamber between the actuator and the droplet ejection nozzle.

One challenge of providing a high density and reliable electrical component is to ensure proper alignment of the cavity and the respective electrical element.

The tolerance stack resulting from the cavity width dimensional tolerance, the cavity etching process variation, the electrical element width dimensional tolerance and the mask to mask alignment tolerance for the entire process, is such that there is a probability that a cavity may be misaligned with respect to the corresponding electrical element. When this occurs, the regions of the electrical element where the misalignment takes place are subject to high stress and are prone to failure.

The issues caused by the misalignment can significantly increase the production costs.

The problem is exacerbated if production is to be moved from a certain wafer size, for example standard 6 inch wafers, to larger wafers, for example 8 inch wafers. The wafer alignment tolerances accompanying each alignment step of the production process are, to a significant degree, directly proportional to the wafer size. Upscaling the size of the wafers in production can, therefore, require, in some cases, some design optimisation.

As mentioned above, some electrical components comprise a plurality of densely packed electrical elements. Attention is drawn to Figure 1 which shows a schematic top view of a part of an electrical component 100 with part of an array of electrical elements 120. In this example, the electrical elements 120 formed on a first surface 110A of a substrate 110 (for example a silicon substrate) are designed to extend lengthwise in a first direction 510 and are arranged in a two dimensional array of two or more rows extending in rows, each row extending in a row direction 500. The two or more rows of the two dimensional array are arranged with respect to each other, in an ‘array’ direction, which, in this case, is perpendicular to the row direction 500 and coincides with the first direction 510. Each electrical element 120 has an individual first electrode 121 and an individual second electrode 122; the first electrode 121 is formed on the substrate 110; the ceramic member 123 is formed on the first electrode 121; the second electrode 122 is formed on the ceramic member, not shown in Figure 1 for the sake of clarity. The electrical connections for the individual first and second electrodes 121 and 122, of the plurality of electrical elements 120, are provided through electrical traces 166 and 160, respectively. The electrical traces 166 and 160 are, in part, routed on the first surface 110A of the substrate 110, between adjacent electrical elements 120, towards the electrical connections 180_a and 180_b. The electrical traces 166 and 160 are arranged to connect the first and second electrodes 121 and 122, respectively, to the electrical connections 180_a and 180_b. The electrical connections 180_a and 180_b connect the electrical traces 166 and 160 to an external circuit and are located in regions that are external to the array of electrical elements. The electrical connections 180_a and 180_b also have different polarities at opposite ends of the array, extending in the first direction 510. Such an arrangement requires the electrical traces 166 or 160, from one row of electrical elements 120, to be routed in the regions between adjacent electrical elements of the adjacent row in the array direction, as shown in Figure 1.

In some cases, the second (top) electrodes 122 may be formed of conductive materials with a lower conductivity with respect to the conductivity of the material of the electrical traces 160. The choice of the material of which the electrodes are formed may be driven by the capability of a material to accomplish specific requirements, for example, good adhesion to the ceramic member or the like, at the partial expense of the conductivity. In such cases, a way of reducing the contribution of the second electrode to the resistance of the electrical connection is to provide more than one connecting point 161, between each individual second electrode 122 and a corresponding trace 160. If two connecting points 161 are provided at opposite ends of the electrode in the first direction 510, the space between adjacent electrical elements is provided with an extra electrical trace. This is shown in Figure 1 where the second electrodes 122 are each provided with two connecting points 161 which are located at either end of the second electrode 122, in the length direction 510. Such an arrangement imposes additional constraints on the level of packing of the electrical elements and on the dimensions of the first electrodes 121, since the first electrodes 121 are formed on the same surface as the electrical traces 166 and 160. This configuration requires even greater precision of the alignment of the electrical elements with the corresponding cavities on the underside of the substrate.

The space free from features that is available between adjacent electrical elements 120 is, therefore, of critical importance. The dimensions of the electrical elements 120 are, usually, already minimised to allow for a high level of packing of the electrical elements 120. The width of the electrical traces 166 and 160 can only be reduced to a certain extent. Narrower electrical traces 166 and 160 in the width direction 501 mean thicker electrical traces 166 and 160 in the thickness direction 505, perpendicular to the first surface 110A, to ensure that the overall electrical resistance is not increased. Increased resistance may lead to production of excess heat and greater likelihood of failure of the electrical traces 166 and 160. Electrical traces 166 and 160 with a reduced width and an increased thickness are more difficult to manufacture and to reliably passivate with passivation layers, because they require the deposition of the passivation layer or layers on an increased vertical surface, in the thickness direction 505.

In order to improve the overall production tolerance and mitigate the adverse consequences of misalignment between the electrical elements and the corresponding cavities it would be advantageous to increase the free space between adjacent electrical elements. This would, in turn, allow a wider first (lower) electrode, thus improving the tolerance of the alignment of the electrical elements and the corresponding cavities.

The present invention provides an improved design of an electrical component with highly packed electrical elements, a design that allows the amount of space occupied by the electrical traces, in the regions between adjacent electrical elements, to be reduced. The present invention aims at improving the above described tolerances and, in turn, the electrical component production yield.

SUMMARY OF THE INVENTION Aspects of the invention are set out in the appended independent claims, while particular variants of the invention are set out in the appended dependent claims.

The present invention provides, in one aspect, an electrical component for a microelectromechanical systems device, the electrical component comprising: i) a substrate comprising a first substrate surface and an opposing second substrate surface spaced apart in a thickness direction perpendicular to the first substrate surface; ii) a plurality of electrical elements arranged over the first substrate surface in rows, each row extending in a row direction, wherein each electrical element comprises: a) a first electrode disposed adjacent to the first substrate surface, b) a ceramic member having a first surface disposed in contact with the first electrode and a second surface opposite the first surface, the ceramic member extending in a length direction that is parallel to the first substrate surface and non parallel to the row direction, and a width direction parallel to the first substrate surface and perpendicular to the length direction; c) a second electrode disposed in contact with the second surface of the ceramic member such that a potential difference may be established between the first and second electrodes and through the ceramic member during operation of the component; d) a passivation layer provided, at least in part, on the second electrode and having vias extending through to the second electrode at opposite ends of the second electrode in the length direction; e) a first electrical trace connecting the first electrode to an external circuit and a second electrical trace connecting the second electrode to the external circuit, wherein each second electrical trace is arranged, at least in part, overlying the respective second electrode and on the passivation layer and each second electrical trace comprises a connecting portion and two electrode connecting points for the respective second electrode, wherein each connecting portion extends in the length direction and is connected to the respective second electrode by said connecting points through said vias of said passivation layer.

In a second aspect the present invention provides a microelectromechanical systems device comprising the electrical component according to the first aspect.

In a third aspect the present invention provides a droplet ejection head comprising the electrical component according to the first aspect.

Further provided is a droplet ejection apparatus comprising a droplet ejection head according to the third aspect.

In yet a further aspect there is provided a method of providing electrical traces to an electrical component for a microelectromechanical systems device.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the drawings, in which:

Figure 1 is a schematic diagram of a top view of a portion of a prior art electrical component;

Figure 2 is a schematic diagram of a top view of a portion of an electrical component according to an embodiment of the invention;

Figure 3 is a schematic diagram of a cross-section of layers forming an electrical element of the electrical component according to an embodiment of the invention. The ends of the electrical element in a first direction are shown;

Figures 4A and 4B are each a schematic diagram of a top view of a variant of an electrical element of the electrical component according to the invention;

Figures 5 A is a schematic cross-section of Figure 1 along the AA’ line; Figures 5B is a schematic cross-section of Figure 2 along the BB’ line;

Figures 6A to 60 depict a series of schematic diagrams of the electrical element depicted in Figure 3 at various stages during the manufacturing process of the electrical component; and

Figure 7 is a schematic diagram of a cross-section of a droplet ejection head according to an embodiment of the invention.

In the Figures, like elements are indicated by like reference numerals throughout. It should be noted that the drawings are not to scale and that certain features may be shown with exaggerated sizes so that these are more clearly visible.

DETAILED DESCRIPTION

An embodiment of the invention and its variants will now be described with reference to Figures 2, 3, 4 A, 4B and 5B.

Figure 2 shows, in top view, a schematic representation of part of one exemplar electrical component 100 according to an embodiment of the invention. Figures 3 and 4 show schematic representations of an exemplar electrical element 120 comprised in the electrical component 100 shown in Figure 2. Figures 4A and 4B show two alternative configurations of the electrical element 120.

Attention is drawn to Figure 2, which is complemented by Figure 3, providing a detailed scheme of an exemplar electrical element 120. The embodiment according to the invention provides an electrical component 100 for a microelectromechanical systems device, the electrical component 100 comprising: i) a substrate 110 comprising a first substrate surface 110A and an opposing second substrate surface 110B spaced apart in a thickness direction 505 perpendicular to the first substrate surface 110A; ii) a plurality of electrical elements 120 arranged over the first substrate surface 110A in rows, each row extending in a row direction 500, wherein each electrical element 120 comprises: a) a first electrode disposed adjacent to the first substrate surface 110A; b) a ceramic member 123 having a first surface disposed in contact with the first electrode and a second surface opposite the first surface, the ceramic member extending in a length direction 510 that is parallel to the first surface 110A and non- parallel to the row direction 500, and a width direction 501 parallel to the first substrate surface 110A and perpendicular to the length direction 510; c) a second electrode 122 disposed in contact with the second surface of the ceramic member 123 such that a potential difference may be established between the first and second electrodes 121 and 122 through the ceramic member 123 during operation of the component; d) a passivation layer 150 provided, at least in part, on the second electrode 122 and having vias 161_a extending through to the second electrode 122 at opposite ends of the second electrode 122 in the length direction 510; e) a first electrical trace 166 connecting the first electrode 121 to an external circuit and a second electrical trace 160 connecting the second electrode 122 to the external circuit, wherein the second electrical trace 160 is arranged, at least in part, overlying the second electrode 122 and on the passivation layer 150 and the second electrical trace 160 comprises a connecting portion 162 and two electrode connecting points 161, wherein the connecting portion 162 extends in the length direction 510 and is connected to the second electrode 122 by said connecting points 161 through said vias 16 l a of said passivation layer 150.

As used herein, “extending in a length direction” means extending in a direction that is different from the row direction 500. Even though the Figures may show electrical elements 120 that are elongated in said length direction 510, this is not limiting in any way. The electrical elements 120 may be formed in any suitable shape and may not be elongated in the length direction 510, and may for example have a length that corresponds to their width, or is even shorter than their width in the width direction 501.

It will also be understood that, while the length direction 510 is shown as perpendicular to the row direction 500, this is in no way limiting. The length direction 510 need only be non-parallel to the row direction 500.

It will further be understood that, while the width direction 501 is shown as coincident with the row direction 500, this is in no way limiting.

As used herein, “during operation” is not limited to the actuation of the element by applying an appropriate potential difference established between the first and second electrodes 121 and 122 and through the ceramic member 123. It also encompasses keeping the electrical element 120 in a resting position, where a potential difference is applied to deform the electrical element 120 and hold it in such deformed configuration.

In the exemplar electrical element of Figure 3, the electrical element 120 is formed on one or more intermediate layers 140 (e.g. 141 and 142) that may form a membrane that is deformed when the electrical element is operated. On the left hand side of Figure 3, the second electrical trace 160 extends to the left of the via 161_a and the connecting point 161, as a lateral portion 163, down the side surface of the ceramic member 123 and then continues horizontally, as a main portion 164, on the intermediate layer 140. The main portion 164 extends to the left over the first substrate surface 110A away from the electrical element and towards the external circuit and reaches the electrical connection 180_a (not shown in Figure 3), as shown in Figure 2, wherein the connection 180_a provides connection to the external circuit. The main portion 164 has a predetermined width in the thickness direction 505 so that the space it takes on the intermediate layer 140 is reduced as much as possible, while still ensuring a reliable electrical connection and a manageable level of heat generation. The lateral portion 163 may have a different shape and/or size with respect to the main portion 164. Preferably, the main portion 164 and the lateral portion 163 have the same cross- sectional area to ensure an equal electrical resistance from the electrical connection 180_a, with the external circuit, to the connecting point 161 that is adjacent to the lateral portion 163.

On the right hand side of Figure 3, the second electrical trace 160 ends with a second connecting point 161. The connecting portion 162 extends between the two connecting points 161. The connecting points 161 are shown, in top view, in Figure 4A as having a circular shape. As the person skilled in the art will understand, this is due to design rules and clearance requirements but is in no way limiting.

Having a second connecting point 161 is very beneficial in reducing the contribution of the second electrode 122 to the electrical resistance and allows a wider choice of materials for the formation of the second electrode 122. As an example, the second electrode 122 may be formed of two superimposed layers of iridium and iridium oxide. Iridium oxide is known to have good adhesion to the ceramic member 123 which is, for example, made of a lead titanate zirconate (PZT) based material; iridium oxide has, on the other hand, a comparatively low electrical conductivity. Adding a layer of iridium on the iridium oxide layer increases the overall conductivity of the second electrode 122 but such conductivity still remains lower than the conductivity of electrodes made, for example, of platinum or gold and, above all, it remains lower than the conductivity of the second electrical trace 160 that may be formed of copper-aluminium alloy, gold or the like. Having a second connecting point 161 connecting the second electrical trace 160 to the second electrode 122, decreases the contribution to the resistance created by the second electrode 122 and renders the connection of the electrical element 120 to the external circuit more efficient.

Having further connecting points 161 connecting the second electrical trace 160 to the second electrode 122 may bring benefit also in the cases where the second electrode 122 has a desirable conductivity, i.e. the same or similar to the conductivity of the second electrical trace 160. Having further connecting points 161, in those cases, may offer redundant connections that will ensure a continued and reliable connection of the second electrode 122 to the external circuit even in the case of a localised failure of one connecting point 161.

In order to mitigate the resistance contribution of the second electrode 122 and/or provide redundant connections, the total number of connecting points 161 provided to each second electrode 122 may be higher than two.

As the person skilled in the art will understand, each connecting point 161 has associated design rule clearances which require a certain amount of conductive material to be deposited on top of and around the via 16 l a. This may add to the stiffness of the second electrode 122 and of the electrical element 120, in general, and may adversely affect the deformation of the ceramic member 123. A balance should, therefore, be reached between the benefits associated with a higher number of connecting points 161 and the flexibility of the electrical element 120.

The presence of the connecting portion 162 of the second electrical trace 160 over the second electrode 122, may itself contribute to increase the stiffness of the electrical element 120, thus negatively affecting its performance. In order to mitigate such an effect, as already discussed, the width in the width direction 501 of the connecting portion 162 of the second electrical trace 160 is set to be as small as possible.

In some embodiments, the main portion 164 and the connecting portion 162 of the second electrical trace 160 have the same cross-sectional area. Preferably, the main portion 164 and the connecting portion 162 have the same thickness in the thickness direction 505. Preferably, the connecting portion 162 has a width in the width direction 501 which is narrower than the width of the main portion 164. More preferably, the ratio of the width of the connecting portion 162 to the width of the main portion 164 is equal to one divided by the number of connecting points 161. This advantageously reduces the impact of the connecting portion 162 on the stiffness of the electrical element while ensuring the same electrical resistance. In embodiments where two connecting points 161 are provided, the width of the connecting portion 162 equals half of the width of the main portion 164.

This does not cause increased heat production when voltage is applied to the electrical element 120 since, depending on the number of connecting points 161, a fraction of the total current is conducted through the connecting portion 162 with respect to the main portion 164.

It will be understood that the second electrical trace 160, between portions 162 and 164, i.e. at the lateral portion 163, may have a different and variable width since it is deposited on the chamfered or vertical part of the electrical element. Preferably, the lateral portion 163 has a constant cross-sectional area.

Providing the connecting portion 162, of the second electrical trace 160, over the second electrode 122 rather than alongside it, frees up space in the region between adjacent electrical elements 120 while still maintaining the benefits of having more than one connecting point 161 between the second electrode 122 and the second electrical trace 160. Providing the connecting portion 162 over the second electrode 122 also allows the first electrode 121 to be widened.

Attention is drawn to Figures 5A and 5B, which compare the routing of tracing in the prior art with those of the invention. Figure 5A shows a schematic cross-section along the line AA’ of Figure 1 whereas Figure 5B shows a schematic cross-section along the line BB’ of Figure 2. As shown in Figure 5 A, limited free space is available in the region 125 between two adjacent electrical elements 120(i) and 120(ii), when two second electrical traces 160 are routed in the region 125. A considerable portion of the region 125 is occupied by the two second electrical traces 160 which also require a suitable distance to be maintained from the first electrodes 121 and 127 in order to ensure an effective insulation of the two second electrical traces 160 from the first electrodes 121 and 127. Figure 5B, on the other hand, shows a significant improvement in the availability of free space in the region 125 since only one second electrical trace 160 is still present in the region 125. The other second electrical trace 160 is located on top of second electrode 122 of the electrical element 121(i) where a cross-section of the corresponding connecting portion 162 is visible. A connecting portion 162 is also visible on top of the second electrode 128 of the electrical element 120(ii).

It is clear from Figure 5B how the invention allows a wider first electrode 121 in the row direction 500 to be designed. A wider first electrode 121 may accommodate a larger tolerance for the alignment of the electrical element 120 with the respective cavity formed below the electrical element 120. In this way, the production yield of an electrical component 100, with tightly packed electrical elements 120, may be increased and production may effectively be moved to greater substrate dimensions that can accommodate a higher number of electrical components 100 but that also carry higher alignment tolerances. This can be achieved while still benefitting from having two separate vias 16 l a connecting the second electrical trace 160 to the second electrode 122.

Even with different designs of the electrical component 100 and with manufacturing methods that do not have an issue with the above described alignment tolerance and, therefore, might not need to widen the first electrode 121, the invention brings significant benefits as it may allow a tighter packing of the electrical elements and/or a reduction in dimension of the electrical component 100 since the distance between the first electrode 121 and the second electrical trace 160 may be reduced.

The position of the connecting portion 162 over the second electrode 122 is not particularly limited. In some embodiments the connecting portion 162 may be formed along a symmetry axis of the electrical element, as shown in Figure 4A. In other embodiments, the connecting portion 162 may be formed away from a symmetry axis. For example, it may be formed on a region at the edge of the second electrode 122, for example, the connecting portion 162_a shown in Figure 4B. Any other position for the connecting portion 162 may be chosen between the symmetry axis as shown in Figure 4A and the edge regions as shown in Figure 4B. If the position of the connecting portion 162 is not along a symmetry axis, as in Figure 4B, the connecting portion 162 may more conveniently be formed of two distinct connecting portions 162 that are symmetrically disposed with respect to the electrical element 120 as a whole, as shown in Figure 4B, where connecting portions 162_a and 162_b are depicted. Having two connecting portions 162_a and 162_b, in this case, might be beneficial so that both edges of the electrical element 120 are subject to the same increase in stiffness and the resulting stress is the same on both edges. If only one connecting portion 162_a or 162_b were present, the corresponding edge of the electrical element 120 might become subject to higher stress than the other edge. This could lead to sub optimal performance of the electrical element 120 and may render the area of the electrical element 120, where the connecting portion 162 is located, more prone to localised damage, like cracks. It will be understood that, depending on the size and shape of the electrical element 120, the position of the connecting portion 162 will be chosen so as to reduce the impact of the connecting potion 162 on the deformation of the electrical element 120 and on the increased resulting stress which affects the electrical element 120. Particular consideration, as to the location of the connecting portion 162, might be given to the areas above the second electrode 122 that are subject to lower stress when operated. As the person skilled in the art will appreciate, the location of those lower stress areas depends on the specific geometry of the electrical element 120. The connecting portion 162 will, therefore, preferably be formed on an area that allows to minimise the impact on the effectiveness of the deformation of the electrical element 120.

As already mentioned, the electrical element 120 comprises a passivation layer 150. In some embodiments the passivation layer 150 may comprise a laminate of passivation layers 151 to 153, for example, as shown in Figure 3.

No passivation is shown in Figure 4 for the sake of clarity. As will be explained below, most of the second electrode 122 and the connecting portion 162 are not covered by the laminate of passivation layers 150: as shown in Figure 3 a window or recess 165 is present in the laminate of passivation layers 150 on top of both the second electrode 122 and the connecting portion 162, so that the laminate of passivation layers 150 does not affect the deformation of the electrical element 120. The location of the window or recess 165 is also shown in dashed line in Figure 4.

As used herein, “window” means a complete removal of the passivation whereas a “recess” means a partial removal of the passivation that results in a passivation of reduced thickness in the thickness direction 505, in the area of the recess. Upon the application of the driving signal, the electrical element 120 deforms in a direction perpendicular to the first surface 110A and away from said first surface 110A. Removing material from above the electrical element 120 will, therefore, contribute to the increase of the extent of deformation of the electrical element 120. It will be understood that the portion of passivation layer or layers 150 located underneath the connecting portion 162, which separates the connecting portion 162 from the second electrode 122, will not be removed. The connecting portion 162 may act as a mask during the removal of the passivation layer 150 from the top of the second electrode 122.

As shown in Figure 3, a layer of passivation 150 is retained on top of the connecting points 161 in order to protect them from the external environment. An additional insulating layer or laminate of insulating layers 170 may be present on top of the passivation layer or layers 150. The insulating layer or laminate of insulating layers 170 may cover the window or recess 165. Preferably, the insulating layer or laminate of insulating layers 170 is arranged to overlie the connecting portion 162. The insulating layer or laminate of insulating layers 170 may be arranged to overlie each of the elements 120 and all the other features present on the first substrate surface 110A. As will be appreciated, the insulating layer may act as a barrier to isolate the electrical component 100 from the external environment and may help protecting the electrical elements 120 and/or electrical connections from chemical attack (e.g. from moisture or ink depending on the particular application of the electrical component).

It will be understood by one skilled in the art, that the electrical element 120 may comprise additional layers further or instead of those described. It will also be understood that some layers may be omitted or combined in a lower number of layers.

In a further aspect the present invention provides a method of providing electrical traces to an electrical component 100 for a microelectromechanical systems device. The method comprises: i) providing a plurality of electrical elements 120 on a first substrate surface 110A of a substrate 110, the plurality of electrical elements 120 being arranged in at least two rows extending in a row direction 500, each of the electrical elements 120 extending in a length direction 510 parallel to the first substrate surface 110A and non-parallel to the row direction 500. Each of the plurality of electrical elements 120 is provided with a first electrode 121 over the first substrate surface, a ceramic member 123, the ceramic members 123 having a first surface in contact with the first electrode 121 and a second surface opposite the first surface, and a second electrode 122 is in contact with the second surface of the ceramic member 123; ii) providing a passivation layer 150 on each second electrode 122; iii) providing a via 16 l a through the passivation layer 150 to the second electrode 122 at opposite ends of each second electrode 122 in the length direction 510; iv) providing a conductive material on the passivation layer 150 and in said vias 16 l a, so as to form a conductive layer over the passivation layer 150 and a connecting point 161 forming a connection to the second electrode 122 through each via 161_a; v) patterning the conductive layer so as to form an electrical trace 160 and to expose part of the passivation layer 150, the electrical trace 160 extending, at least in part, overlying the second electrode 122, to connect to the corresponding second electrode 122 through said vias 16 l a, and forming a connecting portion 162 which extends in the length direction 510 between said vias 161_a.

Preferably the method further comprises the step of: vi) patterning the exposed part of the passivation layer 150 to remove, at least in part, the exposed part of the passivation layer 150 that overlies the second electrode 122.

The method may further comprise forming an insulating layer or laminate of insulating layers 170 overlying the connecting portion 162.

Performing the metal deposition on one or more of the passivation layers 150 allows the second electrode 122 to be protected during the process of patterning the electrical trace 160, in particular the connecting portion 162, as described below with reference to Figures 6A to 60. On the other hand, forming the connecting portion 162 directly on the second electrode 122 or in a trench etched in the passivation layers 150 may severely damage the second electrode 122 when the electrical trace patterning step is carried out, thus compromising the functionality of the electrical element 120.

The method may also comprise removing portions of the substrate, from the side of the second substrate surface, to form cavities in correspondence to the electrical elements formed on the first substrate surface. Such cavities may be formed, for example, through etching or other techniques known in the art.

Figures 6A to 60 are a series of schematic diagrams showing an example of the various stages of the manufacturing process of the electrical element 120 as indicated in Figure 3. For the sake of clarity, only one end of the electrical element 120 in the first direction 510 is shown in figures 6A to 6K because up to the stage of the formation of the vias 16 l a both ends are the same. Figures 6L to 60 show both ends of the electrical element 120 because from this stage onwards the configuration of the electrical trace 160, formed in Figure 6L, is different at the two ends of the electrical element 120 in the first direction 510.

The manufacturing process starts with a substrate 110 comprising a first surface 110A and a second surface 110B which are spaced apart in the thickness direction 505. The material of the substrate is not particularly limited, for example, the substrate 110 may be a silicon wafer.

Figure 6A shows the initial deposition stage in which an intermediate layer 140 is formed on the first surface 110A of the substrate 110. The intermediate layer is formed of sub-layers 141 and 142 deposited on top of each other in the thickness direction 505, as shown in Figure 6B. The layer 141 is, for example, silica (SiCk) formed by thermal oxidation of the silicon wafer. The layer 142 is, for example, made of alumina (AI2O3) deposited by atomic layer deposition (ALD).

Considering now Figure 6C, this shows the stack after the deposition of the first electrode 121 on top of the layer 140. The first electrode 121 may be formed, for example, of platinum (Pt).

Figure 6D shows the stack after the ceramic member 123 has been added on top of the first electrode 121. The thin film ceramic member is, for example, niobium (Nb) doped PZT (PNZT), deposited by sol-gel deposition. The final thickness of the ceramic member 123 may be 2pm.

Next, as shown in Figure 6E, the second electrode 122 is layered on top of the ceramic member 123. The second electrode 122 may, for instance, be another platinum (Pt) electrode deposited according the same procedure as the first electrode 121. Alternatively, the second electrode 122 may be compositionally different to the first electrode 121, for instance, a combination of iridium (Ir) and iridium oxide (IrCk) layers. Together, the first electrode 121, the ceramic member 123 and the second electrode 122 form the electrical element 120.

As may be seen in Figures 6F and 6G, the next steps are patterning of the second electrode 122 and the ceramic member 123 and then of the first electrode 121. The patterning is carried out through dry etch using chlorine (CI2) and argon (Ar) for 4 cycles and a total duration of 2 minutes. The second electrode 122 is patterned first, followed by the lower-lying PNZT and the first electrode 121 layers. Next, as depicted in Figures 6H and 61, a first passivation layer 153 and then a second passivation layer 152 are deposited over all of the exposed surfaces of the stack in the thickness direction 505.

The passivation layer 152 may, for example, be an alumina layer deposited by ALD to a thickness of 80nm. The passivation layer 153 may, for example, be a silica deposited by plasma enhanced chemical vapour deposition (PE-CVD) to a thickness of 200nm.

The layers 152 and 153 are successively patterned as shown in Figure 6J, for example, by lithography.

In Figure 6K, a dielectric via etch is performed to create vias 16 l a at both ends of the second electrode 122 in the first direction 510 and to expose a portion of the second electrode 122 to enable an electrical connection to be formed. Said vias are patterned using standard photolithography and etching processes. In this step a further via, enabling electrical connection to the first electrode 121, is also etched (not shown in this cross- section).

In Figure 6L, metal deposition is performed so that the vias 16 l a and the vias that enable the electrical connection to the first electrodes 121 (not shown) are filled in and a metal layer is formed on top of the passivation layer 152. The metal deposition may, for instance, be carried out by sputtering aluminium (Al), gold (Au), copper (Cu), platinum (Pt), nickel (Ni) and the like or combinations thereof. Thin adhesion layers for the traces may also be deposited prior to or after the formation of the electrical traces.

The first and second electrical traces 166 and 160 (not shown in this cross-section) are formed by patterning the metal layer to the desired width using standard photolithography and etching processes.

Figure 6L shows both ends of the electrical element 120 in the first direction 510 after the formation of the second electrical trace 160. As can be appreciated, on the left hand side of Figure 6L the second electrical trace 160 extends on the left of the via 16 l a and of the connecting point 161 as a lateral portion 163 along the side surface of the ceramic member 123 and, as a main portion 164, on the intermediate layer 140. The main portion 164 extending on the intermediate layer reaches the electrical connection 180_a shown in Figure 2. The main portion 164 has a predetermined width in the thickness direction 505 so that the space it takes on the intermediate layer 140 is reduced as much as possible while still ensuring a reliable electrical connection and a sustainable generation of heat. The lateral portion 163, may have a different shape or size with respect to the main portion 164. Preferably, the main portions 164 and the lateral portion 163 have the same cross-sectional area to ensure an equal electrical resistance to that of the main portion 164 and the lateral portion 163.

On the right hand side of Figure 6L, the second electrical trace 160 ends with the connecting point 161. The connecting portion 162 extends between the two connecting points 161. The connecting portion 162 preferably has the same thickness as the main portion 164 in the thickness direction 505 and a width in the width direction 501 that is half the width of the main portion 164 in the row direction 500. This advantageously reduces the impact of the connecting portion 162 on the stiffness of the electrical element 120 while ensuring the same electrical resistance as the main portion 164 since the connecting portion 162 carries half the current that is carried by the main portion 164.

Turning now to Figure 6M, a third passivation layer 151 is deposited over the entire exposed surface of the stack in the thickness direction 505. The passivation layer 151 is, for example, made of silica deposited by PE-CVD to a thickness of 500nm. The passivation layer 151 is deposited also on the second electrical trace 160.

The passivation layers 151-153 are then etched over the electrical element 120. As seen in Figure 6N, this may provide for the complete removal of the passivation layers 151- 153 over a region overlying the electrical element 120 and the connecting portion 162 so as to form a ‘window’ 165 through to the second electrode 122 on each side of the connecting portion 162, as seen in Figure 4 A. Figure 6N shows that a portion of the passivation layers 151 and 152 is retained between the second electrode 122 and the connecting portion 162. Preferably, the width in the width direction 501 of such retained portion of passivation is the same as the width of the connecting portion 162 in the same direction.

In alternative embodiments, the laminate of passivation layers 150 is only partially removed from above the second electrode 122 and/or the connecting portion 162 so that some passivation is maintained on the second electrode and a recess rather than a window 165 is formed on each side of the connecting portion 162 in the width direction 501. The formation of such a recess may require the use of suitable etches and etch stops such that one of the other layers of the laminate of passivation layers 150 acts as an etch stop. In other embodiments, suitable etch stop layers could be inserted at other points in the stack (e.g. in the thickness direction 505) so as to control the extent in the thickness direction of any such recess.

Such a recess in the laminate of passivation layers 150 is advantageous for substantially reducing the inhibitive effects of the passivation layer 150 on the displacement of the electrical element 120 during operation.

In some embodiments, a window 165 or a recess in a laminate of passivation layers 150 may extend in the width direction 501 to include the whole of the top surface and at least part, preferably all of the lateral surface of each of the one or more electrical elements 120. This configuration is especially advantageous for reducing any inhibitive effects of the passivation layer 150 on the displacement of the electrical element 120 during operation.

As depicted in Figure 6N, the passivation layer 151 is left over the connecting point 161, the lateral portion 163, and main portion 164 of the second electrical trace 160.

Finally, in Figure 60, a continuous insulating layer 170 is deposited over the entire exposed surface of the stack in the thickness direction 505. The insulating layer 170 is, for example, a stack of silica (SiCk) and tantala (TaO_x) layers deposited on top of each other in the thickness direction 505 by atomic layer deposition (ALD) to a total thickness of 20nm.

The insulating layer 170 covers any recess or window 165 present in the underlying passivation layer or laminate of passivation layers 150 overlying each of the one or more electrical elements 120, as well as the connecting portion 162.

After the deposition of the insulating layer 170, a capping layer 103 may be bonded to the electrical component 100 on the insulating layer 170 so that a cavity 106 encloses the electrical element 120, as shown in Figure 7.

A cavity 195 may then be formed in the substrate 110 in correspondence of the electrical element 120 by removing portions of the substrate 110 from the side of the second substrate surface 110B, for example by etching or using any other technique known in the art.

It may be understood by one skilled in the art, that additional manufacturing steps may occur in between the stages depicted in Figures 6A to 60 so as to create other components in other locations of the substrate 110 and that some of these steps may be omitted or split into several sub-steps as may be required.

The electrical component 100 may be used as an actuator in a droplet ejection head. A schematic representation of such droplet ejection head is shown in Figure 7. Figure 7 shows a cross-section of a droplet ejection head 300 in which a fluidic chamber 195 is formed in the first substrate 110, for example, by etching, below the electrical element 120 in the thickness direction 505.

A nozzle plate 196 is provided at the side of the fluidic chamber 195 opposite to the side on which the electrical element 120 is formed, in the thickness direction 505. A nozzle 197 is formed in the nozzle plate 196 to allow ejection of fluid droplets from the fluidic chamber 195. A second substrate 103 defines a recess 106 for the electrical element 120. Such recess 106 may be sealed in a fluid-tight manner so as to prevent fluid within the fluidic chamber 195 and inlet passageways 131 and outlet passageways 132 at either end of the fluidic chamber 195 in the first direction 510 from entering the recess.

The embodiments and their variants described above may be used alone or in combination, as may be, to achieve an improved electrical component according to the invention for specific application requirements.

Claims

1. An electrical component for a microelectromechanical systems device, the electrical component comprising: i) a substrate comprising a first substrate surface and an opposing second substrate surface spaced apart in a thickness direction perpendicular to the first substrate surface; ii) a plurality of electrical elements arranged over the first substrate surface in rows, each row extending in a row direction, wherein each electrical element comprises: a) a first electrode disposed adjacent to the first substrate surface, b) a ceramic member having a first surface disposed in contact with the first electrode and a second surface opposite the first surface, the ceramic member extending in a length direction that is parallel to the first surface and non-parallel to the row direction, and a width direction parallel to the first surface and perpendicular to the length direction; c) a second electrode disposed in contact with the second surface of the ceramic member such that a potential difference may be established between the first and second electrodes and through the ceramic member during operation of the component; d) a passivation layer provided, at least in part, on the second electrode and having vias extending through to the second electrode at opposite ends of the second electrode in the length direction; e) a first electrical trace connecting the first electrode to an external circuit and a second electrical trace connecting the second electrode to the external circuit, wherein each second electrical trace is arranged, at least in part, overlying the respective second electrode and on the passivation layer and each second electrical trace comprises a connecting portion and two electrode connecting points for the respective second electrode, wherein each connecting portion extends in the length direction and is connected to the respective second electrode by said connecting points through said vias of said passivation layer.

2. The electrical component according to Claim 1 wherein each second electrical trace further comprises a main portion extending over the first substrate surface away from the respective electrical element and towards the external circuit, wherein the main portion and the connecting portion of the second electrical trace have the same cross-sectional area.

3. The electrical component according to Claim 2, wherein the main portion and the connecting portion have the same thickness in the thickness direction.

4. The electrical component according to Claim 2 or Claim 3, wherein the connecting portion has a width in the width direction which is narrower than the width of the main portion.

5. The electrical component according to Claim 4, wherein the ratio of the width of the connecting portion to the width of the main portion is equal to one divided by the number of connection points.

6. The electrical component according to Claim 5, wherein the number of connecting portions is two and the width of the connecting portions equals half of the width of the main portion.

7. The electrical component according to any preceding claim, wherein each second electrical trace further comprises a lateral portion extending down a side surface of the ceramic member wherein the lateral portion has a constant cross-sectional area.

8. The electrical component according to any preceding claim, further comprising an insulating layer or laminate of insulating layers arranged to overlie each connecting portion.

9. The electrical component according to any preceding claim, wherein the passivation layer comprises a laminate of plural passivation layers.

10. A method of providing electrical traces to an electrical component for a microelectromechanical systems device, the method comprising: i) providing a plurality of electrical elements on a first substrate surface of a substrate, the plurality of electrical elements being arranged in at least two rows extending in a row direction, each of the electrical elements extending in a length direction parallel to the first substrate surface and non-parallel to the row direction, each of the plurality of electrical elements being provided with a first electrode over the first substrate surface, a ceramic member, each ceramic member having a first surface in contact with the first electrode and a second surface opposite the first surface, and a second electrode in contact with the second surface of the ceramic member; ii) providing a passivation layer on each second electrode; iii) providing a via through the passivation layer to the second electrode at opposite ends of each second electrode in the length direction; iv) providing a conductive material on the passivation layer and in said vias, so as to form a conductive layer over the passivation layer and a connection to the second electrode through each via; v) patterning the conductive layer so as to form an electrical trace for each second electrode and to expose part of the passivation layer, the electrical trace extending, at least in part, overlying the respective second electrode to connect to the respective second electrode through said vias, and forming a connecting portion which extends over the respective second electrode in the length direction between said vias.

11. The method according to Claim 10, further comprising: vi) patterning the exposed part of the passivation layer to remove, at least in part, the exposed part of the passivation layer that overlies each second electrode.

12. The method according to Claim 10 or Claim 11, further comprising forming an insulating layer or laminate of insulating layers overlying each connecting portion.

13. The method according to any of Claims 10 to 12 further comprising removing portions of the substrate from the side of the second substrate surface to form cavities in correspondence to the electrical elements formed on the first substrate surface.

14. A microelectromechanical systems device comprising the electrical component according to any of Claims 1 to 9.

15. A droplet ejection head comprising an electrical component according to any of Claims

1 to 9.

16. A droplet ejection apparatus comprising a droplet ejection head according to Claim 15.