EP1200198A1

EP1200198A1 - Actuator component for a microspray and its production process

Info

Publication number: EP1200198A1
Application number: EP00949481A
Authority: EP
Inventors: Ralf Schnupp; Jochen Thomas
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 1999-08-12
Filing date: 2000-08-10
Publication date: 2002-05-02
Anticipated expiration: 2020-08-10
Also published as: WO2001012340A1; DE50001149D1; JP3598095B2; EP1200198B1; JP2003507168A; DE19938055A1; US6536682B1

Abstract

An actuator component for a piezoelectric microspray comprising a membrane (12) formed in a semiconductor chip (10), a piezoelectric actuator fitted on the surface of the membrane (12), which sets the membrane vibrating, and a tube (14) attached to the semiconductor chip which conducts the liquid to be atomized from an inlet port to the piezoelectric actuator on the opposite surface of the membrane. A microspray using this sort of actuator component is comprises a holding device to which this sort of actuator component is fixed, so that the inlet is directly connected to the fluid by means of a liquid-conducting tube; exceptionally, the pipe is connected to the liquid duct and piezoelectric actuator beside surface of the membrane by means of the holding device. Said holding device has an opening around the surface zone of the membrane opposite the actuator for the discharge of atomized liquid.

Description

Actuator member for a micro atomizer and process for its manufacture

description

The present invention relates to an actuator member for a micro atomizer and in particular to an actuator member for a piezoelectrically operated micro atomizer, to methods for producing such an actuator member and to a micro atomizer using such an actuator member.

Elements for atomizing liquid media, which are referred to below simply as atomizers, are used in many technical areas, for example the cosmetics industry for atomizing hair sprays and perfumes, in medicine as medicament sprays, with different coating techniques for atomizing paints and adhesives chemistry for nebulizing liquid reagents, and in the field of domestic technology as room humidifiers.

A large part of the atomizers currently used works by means of mechanical atomization, in which the liquid is pressed through a mechanically generated overpressure through a valve of suitable shape and size. This causes the medium to flow, i.e. the liquid to be atomized is usually distributed statically in small droplets and forms a liquid mist. The overpressure required is manually activated by a pumping process, for example in the case of perfume atomizers, or by using overpressure reservoirs, e.g. Propellant gas in hair sprays.

In addition to the mechanical systems described above, there are also electrically driven nebulizers based on piezoelectric substrates that are electrically excited to vibrate. One is on the surface of the Liquid located in the piezoelectric substrate is atomized by the resulting capillary waves.

In "Micromechanical Ultrasonic Liquid Nebulizer", by R. Paneva et al., Sensors and Actuators A 62 (1997), pp. 765 to 767, a piezoelectric atomizer is described in which a thin silicon membrane vibrates through a piezoelectric ZnO layer is displaced, with liquids being atomized by the thin silicon membrane. The atomizer described in this document operates at an oscillation frequency of 80 to 86.5 kHz, the atomizer disclosed there producing droplets of widely differing diameters.

All existing mechanical as well as piezoelectric systems have a major disadvantage in that the droplet diameters vary within a wide range. This is a major disadvantage, particularly in medical applications. In order for droplets to be absorbed by the lungs, they must have a diameter of approximately 1 to 5 μm. All known systems achieve this only to a certain extent, so that the effectiveness of the atomizers on the market is only 10% to a maximum of 15%. This means that with the known atomizers, ten times the volume has to be atomized in order to transport the amount of medication necessary for the patient into the lungs. In addition, the volume of individual dosing processes to be atomized fluctuates over a wide range in the known atomizers.

All known mechanical atomizers also have the disadvantage that nozzles must be used which are very susceptible to clogging. For this reason, mechanical systems are always a disposable product. The use of nozzles also increases the likelihood of incorrect operation, which is particularly unfavorable or even dangerous from a medical point of view in acute situations. In "Liquid atomization by ultrasound", in Electronics 10/1979, pages 83 to 86, the ultrasound atomizing effect is described, which works according to the principle of capillary wave theory.

DE 19802368 C1 describes a microdosing device in which a pressure chamber is delimited on one side by a membrane, an inlet opening and an outlet opening being provided in the pressure chamber. A suitable control of the membrane causes fluid to be sucked in through the inlet opening for a dosing process and to be expelled through the outlet opening. This microdosing device works on the basis of a displacement effect and not on the basis of the capillary wave theory.

From DE 69404004 T2 a piezoelectric nebulizer is known in which liquid is applied to an atomizing grid that is set in vibration using a soft organ with a capillary or felt-like structure, such as an open-cell foam.

The object of the present invention is to create a micro-atomizer which, on the one hand, enables mass production and, on the other hand, enables atomization of droplets having a defined diameter with increased efficiency, and to provide a method for producing such a micro-atomizer.

This object is achieved by a micro-atomizer according to claim 1 and a method for producing a micro-atomizer according to claim 13.

The actuator member used in the atomizer according to the invention uses the piezoelectric principle. In this case, a piezoelectric layer, preferably produced using thin-film technology, is used to deflect a thin membrane, which is preferably etched in silicon Vibrations is set. In the silicon substrate in which the membrane is formed, a channel device is also formed which serves to supply the liquid to be atomized in order to effect a substantially uniform wetting of the surface of the membrane opposite the piezoelectric actuator. The supply of liquid through the channel device provided according to the invention, such that the membrane is wetted essentially uniformly, prevents according to the invention that the droplet diameters vary within a wide range. The actuator member of the atomizer according to the invention is preferably suitably adapted to be operated at a frequency between 2 and 2.5 MHz, and in such a way that the droplets produced by the atomization have a diameter between 1 and 5 μm. For this purpose, the geometric dimensions of the membrane, the liquid supply and the vibration frequency used are suitably adapted as atomization parameters in order to set a desired droplet size.

Depending on the size of the membrane, it can be advantageous according to the invention to design the channel device in such a way that it supplies the liquid to be atomized to the membrane from different directions. For example, the membrane can be rectangular, the channel device feeding the liquid to be atomized via the four corners of the membrane.

A micro atomizer according to the invention using such an actuator member can comprise a holder to which the actuator member is fixed in such a way that the inlet end is fluidly connected to a liquid supply line such that the channel device, with the exception of a fluid connection thereof, to a liquid supply line and to the piezoelectric actuator opposite surface of the membrane is sealed by the holder, and that in the region of the surface of the membrane opposite the piezoelectric actuator, an opening of the holder is provided for ejecting the atomized liquid - D -

The holder is designed in such a way that the actuator member can be easily attached to it, the liquid supply line preferably leaving the holder in a direction which is opposite to the direction of ejection of the atomized liquid.

Furthermore, the present invention provides a method for producing a piezoelectrically operated micro-atomizer, in which a piezoelectric actuator is first applied to a main surface of a semiconductor substrate, whereupon the main surface of the semiconductor substrate opposite the piezoelectric actuator is structured around a membrane on which the piezoelectric Actuator is arranged, and to fix a channel device, which extends from an inlet end to the membrane, in the same. The actuator member is fixed to a holder such that the surface of the membrane opposite the piezoelectric actuator is facing an opening in the holder.

The present invention thus creates an actuator member for a piezoelectrically operated micro atomizer which, through the use of micromechanics, and in particular silicon technology, enables a very small and inexpensive system which can be produced in very large numbers. Due to the properties of the atomizer described above, the droplet distribution, the precision of the volume to be atomized and, in the case of a medical application, the medical effectiveness are considerably improved. The actuator member does not require the use of a nozzle, so that signs of constipation cannot occur. The system is thus also suitable for multiple use, for example only one liquid container connected to the liquid supply line has to be replaced. Due to the low power requirement of the piezo drive, the energy consumption need reduced.

Further developments of the present invention are set out in the dependent claims.

Preferred exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. Show it:

Fig. La) is a schematic perspective view of an embodiment of an actuator member according to the invention;

Fig. Lb) is a schematic perspective view of a holder of a micro-atomizer according to the invention;

2a) and 2b) are schematic representations to explain different exemplary embodiments of channel devices of actuator components according to the invention; and

3a) to 3e) are schematic sectional views to illustrate the method according to the invention for producing an actuator member.

FIG. 1 a) shows a schematic perspective view of an exemplary embodiment of an actuator member in which a membrane 12 is formed in a main surface of a silicon substrate 10. A schematic top view of the exemplary embodiment shown in FIG. La) is also shown in FIG. 2a), the following description being continued with reference to FIGS. La) and 2a). The atomizing surface of the membrane 12 can be seen in each of these figures, so that the piezoelectric actuator arranged on the opposite surface of the membrane cannot be seen in these figures. The piezoelectric actuator is used to vibrate the membrane 12. In the Furthermore, a channel device 14 is formed on the substrate surface, which has the recess through which the membrane 12 is fixed, and enables a liquid to be atomized to be supplied to the atomizing surface of the membrane 12. Furthermore, a recess 16, which serves as a media inlet, is provided in this main surface of the silicon substrate 10.

The channel device 14 provides a fluid connection between the media inlet 16 and the atomizing surface of the membrane 12 in order to enable a substantially uniform wetting of the atomizing surface with the liquid to be atomized. For this purpose, in the exemplary embodiment shown, the channel device 14 has channel sections 14a, 14b, 14c and 14d which feed the liquid to be atomized from the direction of the four corners of the substantially rectangular membrane 12 to the atomizing surface thereof. It should be noted that in the exemplary embodiment shown, the membrane 12 is fixed by a membrane recess, which was formed by means of a KOH etching process, so that the side walls 18 of the membrane recess have the bevel which can be seen in FIG 55 degrees. As can also be seen, the sections 14a, 14b, 14c and 14d of the channel device 14 each end in the upper region of the inclined side surfaces 18 such that the medium to be atomized is supplied via the inclined side surfaces 18. It should also be noted that the media inlet recess 16 and the channel device 14 can also be formed by KOH etching.

The actuator member formed in this way, as shown, for example, in FIG. 1 a), is now introduced into a holder, for example as shown in FIG. 1 b), to build up a micro-atomizer. For this purpose, the holder 20 has a receiving compartment 22, into which the actuator member is inserted and in which the same can be fixed in a suitable manner. For this purpose, the bracket 20 preferably protrusions 24 and 26 that hold the actuator member. Furthermore, the holder 20 is designed such that it forms closed channels together with the actuator member, which are fluidly connected to the atomizing surface of the membrane 12 and the media inlet 16. The holder 20 preferably also has a device 28 for connecting a liquid line 29, preferably a hose, in such a way that the liquid line 29 is fluidly connected to the media inlet 16. The holder 20 also has an opening 30 which, when the actuator member is mounted in the holder 20, is arranged above the atomizing surface of the membrane 12, so as to enable the atomized liquid to be ejected. The liquid line 29 is preferably arranged with respect to the opening 30 in such a way that the opening 30 is arranged, for example, in an inhalation channel of an inhaler. For this purpose, the liquid line 29 preferably leaves the holder 20 opposite the opening 30, as shown in FIG. 1b). In alternative exemplary embodiments, the opening 30 can be provided with a grid which, for example, ensures a precisely defined droplet size or allows the system to be operated overhead.

The actuator member shown in Fig. La) is preferably made of silicon, while the holder shown in Fig. Lb) made of plastic, which is advantageous in terms of the system price, or any other suitable material. The actuator member can be attached to the holder, for example, by means of anodic bonding processes, and in addition, such anodic bonding processes also enable a very strong, tight and stable connection to another silicon chip, which in turn can contain suitable channels and liquid connections.

In the holder shown in Fig. Lb) is a possibility for fluid connection in dashed lines the device 28 for connecting a liquid line to the media inlet 16 is shown. It should be noted that the provision of a corresponding recess 32 in the holder 20 means that the media inlet recess 16 in the substrate 10 of the actuator member can be dispensed with if the channel device 14 ends under the recess 32, so that a fluid connection is thereby ensured.

in operation, the atomizing surface of the membrane 12 is uniformly wetted with the liquid to be atomized via the liquid line 29, the media inlet 16 and the channel device 14. For this purpose, the liquid line 29 is connected to a liquid reservoir (not shown), which is preferably an overpressure container which can be fluidly connected to the liquid line 29 via a valve. The membrane 12 is vibrated by the piezoelectric actuator, so that the liquid located on the atomizing surface of the membrane 12 is atomized on the basis of the capillary wave theory. During the atomization process, atomization liquid is continuously supplied via the channel device 14.

By means of this procedure, atomization can be carried out by the actuator member according to the invention, which results in droplets whose diameters do not vary in a large range, but whose diameters in a defined range, for medical technology preferably between 1 and 5 μm. Droplets of this order of magnitude are obtained using an excitation frequency of the piezeoelectric actuator in the range from 2.0 to 2.5 MHz, the exact value of the excitation frequency having little dependence on the viscosity of the liquid to be atomized.

2b) shows a schematic top view of a channel device 34, as it can be sufficient for a membrane 36 of small size, in order to ensure even wetting to effect the same with the liquid to be atomized. The channel device 34 is in turn fluidly connected to a recess 16 which defines a media inlet. The arrangement shown in FIG. 2b) is suitable for atomizing small fluid volumes, while the embodiment shown in FIG. 2a) is suitable for atomizing larger fluid volumes.

The channels 14 and 34 act in addition to the liquid supply due to the narrowing of the cross section also as a flow restriction. With a constant outlet pressure of the liquid and through the channels produced with a precise cross-section, a constant flow to the piezoelectric membrane 12 or 36 is established. It should be noted that the channels according to the present invention can be precisely etched using silicon technology, so that a defined supply of the liquid to the atomizing surface of the membrane is possible. Thus, the microactuators can be specifically adjusted to the desired flow quantities by means of differently selected cross sections, so that the atomization of very precisely defined volumes is possible.

When used in medical applications, the biocompatibility of the components that come into contact with the liquids must be taken into account. Exposed surfaces that can come into contact with the liquids are provided with a protective layer, which preferably consists of titanium or titanium nitride.

A method for producing an actuator member according to the invention is described below with reference to FIGS. 3a) to 3e).

A single-crystalline silicon substrate 10, which can be n- or p-doped, is preferably used as the base material for the actuator member. An ion implantation, for example with phosphorus, is carried out on a surface of the silicon substrate 10 in order to produce a membrane layer 40. A p-silicon is preferably used as the silicon substrate 10, while the layer 40 is an n-type layer. Layer 40 later also serves as the lower electrode for driving the piezoelectric layer. The substrate 10 on which the implantation layer 40 is arranged is subsequently subjected to an oxidation in order to produce SiO 2 layers 42 and 44. The resulting layer composite is shown in Fig. 3a).

A masking layer 46 is now formed on the back, which preferably consists of silicon nitride Siß ^ and is preferably formed by a chemical deposition, for example LPCVD (= Low Power Chemical Vapor Deposition). An opening 48 is formed in the upper oxide layer 42 for later contacting of the implantation layer 40, see FIG. 3b).

The lower oxide layer 44 and the silicon nitride layer 46 are structured, for example by photolithographic methods, in order to define an opening 50 for the later etching free of the membrane recess from the underside of the silicon substrate 10. Above this opening 50, a piezoelectric material 52 is applied to the upper oxide layer 42, which acts as a piezoelectric actuator in the finished component. The piezoelectric material can consist of AlN, PZT or ZnO, for example. This results in the structure shown in FIG. 3c).

Subsequently, metallizations 54 and 56 for the electrical control of the piezoelectric element 52 are produced on the top of the structure shown in FIG. 3c), see FIG. 3d), whereupon a passivation layer 58 is applied and structured to openings 60 and 62 for contacting the To define metallizations 54 and 56, see Fig. 3e). Subsequently, a KOH etching, delimited by the masking layers deposited on the front and rear, is carried out from the rear up to the implantation layer 40, which serves as an etching stop that the membrane 12, which is formed in the implantation layer 40, is produced.

Although not shown in FIG. 3, during this KOH etching the integrated flow channels with a shallower depth and the necessary depressions for the media inlet can be produced at the same time. Alternatively, starting from the state shown in Fig. 3e), the lower mask layers 44 and 46 are further patterned to define the channels and the media inlet, whereupon a further KOH etching is carried out to the channels and the media inlet in the back of the silicon substrate 10 to generate.

Although a preferred exemplary embodiment of the method according to the invention for producing an actuator element has been described above with reference to FIG. 3, it is obvious to those skilled in the art that a different order of the steps described above can be used to determine the structure of the actuator element according to the invention, as is shown, for example, in FIG . la) is shown to produce in a main surface of a silicon substrate and furthermore a piezoelectric drive on the opposite main surface of the silicon substrate.

According to the invention, it is only essential that the recess, which defines the membrane, and the feed channels, which ensure uniform wetting of the atomizing surface of the membrane, are formed in the same main surface of a silicon substrate, so that the present invention makes the mass production of actuator components of small size inexpensive and with low energy consumption.

Claims

claims

1. Piezoelectrically operated capillary wave micro-atomizer with the following features:

a membrane (12; 36) formed in a semiconductor substrate (10);

a piezoelectric actuator (52) arranged on a surface of the membrane (12; 36) in order to vibrate the membrane (12; 36); and

a channel device (14; 34) formed in the semiconductor substrate (10) for supplying a liquid to be atomized from an inlet end to the surface of the membrane (12; 36) opposite the piezoelectric actuator (52), the oscillations of the membrane (12 36) the liquid supplied to the surface of the membrane is atomized on the basis of the capillary wave theory and is expelled through an outlet (30) arranged opposite the membrane.

2. Micro atomizer according to claim 1, wherein the membrane (12; 36) and the channel device (14; 34) are formed by recesses in a first main surface of the semiconductor substrate (10).

3. Micro atomizer according to claim 1 or 2, in which in the first main surface of the semiconductor substrate (10) further a recess defining a liquid inlet (16), which is fluidly connected to the inlet end of the channel device (14; 34), is formed.

4. Micro atomizer according to one of claims 1 to 3, in which the channel device (14; 34) is designed to to effect a uniform wetting of the surface of the membrane (12; 36) opposite the piezoelectric actuator (52).

5. Micro atomizer according to one of claims 1 to 4, in which the channel device (14) is designed to bring about a supply of a liquid to be atomized to the membrane (12) from different directions.

The micro-atomizer according to claim 5, wherein the membrane (12) has a rectangular shape, the channel device (14) having channel sections (14a, 14b, 14c, 14d) for the liquid to be atomized over the four corners of the membrane (12 ) feed.

7. Micro atomizer according to one of claims 1 to 6, in which the piezoelectric actuator (52) causes the membrane (12; 36) to vibrate at a frequency between 2 and 2.5 MHz, such that the droplets generated by the atomization one Have diameters between 1 and 5 μm.

8. Micro atomizer according to one of claims 1 to 7, in which the channel device (14; 34) is designed as a defined flow restriction.

9. Micro atomizer according to one of claims 1 to 8, which has a holder (20) on which the semiconductor substrate is fixed in such a way that

the inlet end is fluidly connected to a liquid supply line (29);

the channel device (14; 34), with the exception of a fluid connection thereof with the liquid supply line (29) and the surface of the membrane (12) opposite the piezoelectric actuator (52), is sealed by the holder (20); and

In the area of the surface of the membrane (12) opposite the piezoelectric actuator (52), an opening (30) of the holder (20) is provided for ejecting the atomized liquid.

10. Micro atomizer according to claim 9, wherein the opening (30) is provided with a grid.

11. Micro atomizer according to claim 9 or 10, wherein the liquid supply line is arranged such that it leaves the holder (20) in a direction opposite to the direction of ejection of the atomized liquid.

12. Micro atomizer according to one of claims 9 to 11, wherein the holder (20) has a recess serving as a liquid inlet (32).

13. A method for producing a piezoelectrically operated capillary wave theory micro-atomizer for atomizing a liquid supplied to a surface of a membrane on the basis of capillary wave theory, with the following steps:

a) Generation of an actuator member by the following substeps:

al) applying a piezoelectric actuator (52) to a main surface of a semiconductor substrate (10, 40);

a2) structuring the main surface of the semiconductor substrate opposite the piezoelectric actuator (52), around the membrane (12) on which the piezoelectric actuator (52) is arranged, and a channel device (14; 34) which extending from an inlet end to the membrane (12; 36) to define therein; and

c) fixing the actuator member to a holder (30) so that the surface of the membrane opposite the piezoelectric actuator faces an opening in the holder.

14. The method according to claim 13, wherein in step a2) further structures at the inlet end of the channel device (14; 34) with the same fluidly connected liquid inlet (16) in the surface of the semiconductor substrate (10, 40) opposite the piezoelectric actuator (52) becomes.

15. The method according to claim 13 or 14, wherein the membrane (12) is formed by a KOH etching, the channel device producing up to the oblique side walls (18) formed by the KOH etching of the recess defining the membrane (12) becomes.