JP4715641B2 - Material for MEMS device, method for manufacturing the material, and MEMS device including the material - Google Patents

Description

  The present invention relates to a material for a microelectromechanical system (MEMS) device and a MEMS device including the material.

  A MEMS device including an electromagnetic fine actuator generally requires a fine structure having a thick magnetizable film. Thick films are formed around the microactuator during operation and are necessary for the associated magnetic fields that are strong enough for the operation.

  The advantage of such a membrane is that the material forming the film can be rapidly deposited by electrolysis. However, the disadvantage of such thick films is that the in-plane film stresses are inherently high. This causes delamination during the heat treatment and breaks the film.

  An example of this type of membrane is Singapore Patent Application No. 20003718-8. This application was filed before the application of this specification, but has not yet been published at the time of filing of this specification. This earlier application describes cobalt-nickel-rhenium-tungsten-phosphorous (Co-Ni-Re-WP) formed by electrodeposition as a hard magnetic film with high perpendicular magnetic anisotropy suitable for use in MEMS devices. ) Is disclosed. However, the disadvantage of such a composition is that its magnetic properties degrade when exposed to high temperatures. For example, it was observed that the perpendicular remanent magnetization Mr and the perpendicular coercive force Hc of the Co—Ni—Re—WP composition were significantly deteriorated when annealed at a temperature of 200 ° C. for 2 hours in the ambient atmosphere.

  An object of at least some embodiments of the present invention is to address such delamination and degradation of magnetic properties.

  According to a first aspect of the present invention, there is provided a multilayer material used in a microelectromechanical system (MEMS) device, wherein the material is cobalt, nickel, rhenium, tungsten, and phosphorus (Co—Ni—Re—W). A plurality of layers of magnetizable material having -P), the adjacent or each set of Co-Ni-Re-WP layers having multiple layers of non-magnetizable electrically conductive material therebetween Material is provided.

  By providing a plurality of Co-Ni-Re-WP layers rather than a single thick layer, the layer of material can be thinner than a single thick layer. As a result, multilayer materials tend not to have the disadvantages of weak mechanical properties and thermal instability that appear in a single layer. Instead, the resulting material is an improved material that provides high and stable out-of-plane magnetic properties. Thus, this multilayer material is particularly suitable for the fabrication of MEMS devices and the low temperature annealing often involved in the process.

  According to a second aspect of the present invention, a multilayer material used in a microelectromechanical system (MEMS) device, the material being magnetizable having cobalt, platinum, and phosphorus (Co—Pt—P). A set of adjacent or each Co-Pt-P layer comprising a plurality of layers of material is provided with a multilayer material having each layer of non-magnetizable electrically conductive material therebetween.

  The advantages derived from the first aspect of the present invention are the same as the advantages of the second aspect.

  Preferably, said multilayer material has at least five layers of magnetizable material, each layer being adjacent to said or each layer of magnetizable material by each layer of non-magnetizable electrically conductive material It is away from. More preferably, 5 to 10 layers of the magnetizable material are formed. For example, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers, or 10 layers are formed.

  In certain embodiments, the multilayer material includes a base layer of the or another non-magnetizable electrically conductive material. The base layer can be a seed layer that bonds the remaining portion of the multilayer material to a substrate. A chromium (Cr) layer may be provided between the base layer and the substrate. Thus, in these embodiments, each layer of magnetizable material is a layer on each layer of electrically non-magnetizable material.

  Preferably, the layers of magnetizable material are each at least 0.1 μm and preferably have a thickness of less than 2 μm. Preferably, the layers of magnetizable material each have a thickness in the range of 0.5 μm to 1.5 μm. Preferably, the layers of magnetizable material each have a thickness of approximately 1 μm.

  Preferably, the layers of non-magnetizable electrically conductive material disposed between adjacent sets of layers of magnetizable material are each at least 0.1 μm, preferably less than 0.5 μm thick Have The layers of non-magnetizable electrically conductive material can each have a thickness of approximately 1 μm.

  Preferably, the base layer is a thinner layer and can be approximately 200 nm thick. The chromium (Cr) layer can have a thickness of approximately 20 nm.

  The non-magnetizable electrically conductive material can be, for example, gold (Au) or copper (Cu). Preferably, when the layer of magnetizable material is Co-Ni-Re-WP, the non-magnetizable electrically conductive material between adjacent Co-Ni-Re-WP layers is Cu It is. Preferably, when the layer of magnetizable material is Co—Pt—P, the non-magnetizable electrically conductive material between adjacent sets of Co—Pt—P layers is Au. Preferably, the seed layer is Au.

  According to a third aspect of the present invention there is provided a structure comprising a multilayer material as defined above, and further comprising a substrate.

  Preferably, the substrate is a glass substrate.

  According to a fourth aspect of the present invention there is provided a microelectromechanical system (MEMS) device comprising a structure as defined above and / or a multilayer material as defined above.

  According to a fifth aspect of the present invention, there is provided a multilayer material used in a microelectromechanical system (MEMS) device, wherein the material includes a plurality of layers of magnetizable materials, and the adjacent or each magnetization A set of possible material layers has each layer of non-magnetizable electrically conductive material in between, at least the layer of magnetizable material is a multilayer material having a thickness in the range of 0.1 μm to 2 μm Is provided.

  The magnetizable material may comprise Co—Ni—Re—WP. The magnetizable material may comprise Co—Pt—P.

  The features that can be selected in the first to fourth aspects of the invention defined above are the same as the features that can be selected in the fifth aspect.

  According to a sixth aspect of the present invention, there is provided a method for producing a multilayer material for use in a microelectromechanical system (MEMS) device, the method comprising a plurality of layers of magnetizable material and non-magnetizable electricity. A plurality of layers of conductive material, such that different layers alternate with each other on top of each other, and a set of adjacent layers of said or each magnetizable material has each layer of non-magnetizable electrically conductive material therebetween In addition, a method for producing a multilayer material including a forming step is provided.

  The layer of magnetizable material can be, for example, Co—Ni—Re—WP or Co—Pt—P. Preferably, the layers of magnetizable material are all made of the same material.

  The method can include forming a first layer of multilayer material on a substrate. The first layer is preferably a seed layer.

  The method may include forming the layer of magnetizable material and / or the non-magnetizable layer of electrically conductive material by electroplating. Preferably, the method includes the step of forming the non-magnetizable layer of electrically conductive material by electroless plating. Preferably, the plating is performed by placing the substrate in an electrochemical bath, and preferably the manufacturing method includes the step of placing the substrate in such a bath. Preferably, the bath is set to a temperature lower than 30 ° C, but may be any temperature between room temperature and 100 ° C. Preferably, the bath has a pH of 5.0 or less.

  The features of the first to fifth aspects of the present invention can also be the characteristics of the sixth aspect.

  Specific embodiments of the present invention will be described with reference to the accompanying drawings.

  This specific description begins with a description of the structure that specifically represents the present invention, and also describes a method of forming that structure that also specifically represents the present invention.

  FIG. 1 is a schematic diagram of a structure 10 that includes a multilayer material 20. The structure 10 is used in a MEMS device (not shown). The structure 10 includes a glass substrate 30 having a thin chromium (Cr) layer 40 formed thereon. In the present embodiment, the Cr layer 40 is approximately 20 nm thick. A thick layer 50 of gold (Au) is formed over the Cr layer 40 and serves as a seed layer for the remainder of the multilayer material. In the present embodiment, the Au seed layer 50 is approximately 200 nm thick. The remaining portion of the multilayer material 20 includes alternating magnetizable Co—Ni—Re—WP layers 60 and non-magnetizable but electrically conductive Cu layers 70. The first layer on the Au seed layer 50 is a first Co—Ni—Re—WP layer. In the present embodiment, the multilayer material includes six Co—Ni—Re—WP layers 60 and five Cu layers 70. Therefore, the multilayer material layer farthest from the glass substrate 30 is the Co—Ni—Re—WP layer 60.

  To manufacture the example structure shown in FIG. 1, the following method was performed.

A plating bath aqueous solution was prepared for electroplating the Co—Ni—Re—WP layer 60 and the Cu layer 70. The bath for the Co—Ni—Re—WP layer 60 consists of 0.4 M boron hydroxide (B (OH) ₃ ), 0.4 M sodium chloride (NaCl), 0.05 M cobalt chloride hexahydrate. (CoCl ₂ · 6H ₂ O), 0.05 M nickel chloride hexahydrate (NiCl ₂ · 6H ₂ O), 0.007 M ammonium perrhenate (NH ₄ ReO ₄ ), 0.001 M tungstic acid sodium dihydrate _{(Na 2 WO 4 · 2H 2} O), and was composed of sodium phosphite 2.5 hydrate of _{0.017M (NaH 2 PO 3 · 2.5H} 2 O). The bath for Cu layer 70 is 0.315 M hydrogen sulfide pentahydrate (CuSO ₄ .5H ₂ O), 0.2 M sodium pyrophosphate decahydrate (Na ₄ P ₂ O ₄ .10H ₂ O). , And 1.6 M sulfuric acid (H ₂ SO ₄ ). All solutions were prepared with demineralized pure water. The pH of the bath solution for the Co—Ni—Re—WP layer 60 was adjusted to approximately 4.5 using sodium hydroxide (NaOH) and sulfuric acid (H ₂ SO ₄ ). The Cu bath solution for the non-magnetizable Cu layer is acidic at a pH of approximately 0.1.

  A clean glass substrate, substantially the same as the glass substrate 30, was first sputtered with chromium (Cr) to a thickness of approximately 20 nm to form a Cr layer 40 on the substrate. Subsequently, gold (Au) was sputtered to a thickness of approximately 200 nm to form a seed layer 50 on the Cr layer 40. The surface of the seed layer 50 on each substrate 30 was cleaned using sulfuric acid and activated.

  Following cleaning and activation of the seed layer, a Co—Ni—Re—WP layer 60 and a Cu layer 70 were alternately formed on the seed layer 50 one after another by electrochemical deposition. The method used was electrolytic plating or electroless plating (chemical plating). Thus, the laminated material 20 was formed.

The Co—Ni—Re—WP layer 60 was deposited at room temperature at a direct current density of 25 mA / cm ² by electrolytic plating using a rotating disk electrode (RDE) mechanism. A platinum wire was used as the anode for plating of each layer. A silver / silver chloride (Ag / AgCl) reference electrode was used as the reference electrode and connected to the plating solution via a salt bridge. In order to obtain good uniformity of the deposited layer, the electroplating was performed with the rotation speed of the substrate 30 being 500 rpm.

It is expected that the Cu layer 70 can be deposited on the magnetizable Co—Ni—Re—WP layer 60 using either electrolytic plating or electroless plating from a Cu electrolytic solution. When plating by electrolysis, a DC current density of 25 mA / cm ² and a rotation speed of 500 rpm were used in order to match the conditions with the above Co—Ni—Re—WP plating. Therefore, electrolytic plating was performed using RDE and platinum as the anode at room temperature. A silver / silver chloride (Ag / AgCl) reference electrode was again used as the reference electrode and connected to the Cu plating bath via a salt bridge.

  In order to study the simplification of the multilayer plating procedure of the present application, as a comparative study, electroless plating (chemical plating) of Cu was performed on Co—Ni—Re—WP. The electroless plating process procedure is quite simple compared to Cu electrolytic plating because no current source is required. After plating each Co—Ni—Re—WP layer 60, a relevant substrate 30 is simply immersed in Cu electrolyte for a controlled period of time on the Co—Ni—Re—WP layer. Cu was formed by electroless plating.

  The multilayer film material derived from the electroplated Cu layer 70 is hereinafter referred to as multilayer 1 or ML1. The multilayer film material resulting from the electroless plating (chemical plating) of the Cu layer 70 is referred to as multilayer 2 or ML2.

The film thickness of the magnetizable Co—Ni—Re—WP layer 60 was adjusted by controlling the plating time. FIG. 2 is a graph showing the relationship between the thickness of the Co—Ni—Re—WP layer deposited by the above-described electrolytic plating method and the time of electrolytic plating for forming the layer. As can be seen from FIG. 2, the film thickness of Co—Ni—Re—WP changes almost linearly with the plating time under the same plating conditions. At a current density of 25 mA / cm ² and a stirring speed of 500 rpm, Co—Ni—Re—WP was precipitated at a rate of approximately 0.45 μm / min. Therefore, the layer thickness could be easily controlled by controlling the time of the electroplating operation. As shown in Table 1, the Co—Ni—Re—WP layer 60 has a Cu film (the associated Cu layers), regardless of whether it is a layer in ML1 material or ML2 material. Regardless of whether 70 was electrolytically or electrolessly plated (chemically plated), it was plated for the same 120 seconds. As a result, the film thicknesses of the magnetizable layers 60 are substantially the same. Each Cu intermediate layer 70 was plated for 60 seconds, regardless of whether it was ML1 electroplated film 70 or ML2 electrolessly plated (chemically plated) film. For comparison, a thin single layer of Co—Ni—Re—WP and a separate thick single layer of Co—Ni—Re—WP are 120 seconds and 25 mA / cm ² and 500 rpm, respectively. Electrolytic plating was performed with a plating bath solution for 720 (120 × 6) seconds. These single layer comparative materials are not listed in Table 1.

  The magnetic properties of each sample were measured using a sample vibration magnetometer (VSM). Table 2 shows the absolute saturation magnetization Ms, absolute residual magnetization Mr, coercive force Hc, and rectangular ratio S (Ms / Mr) in the out-of-plane (perpendicular) direction before and after annealing at 200 ° C. for 2 hours in the ambient atmosphere. This is a summary. The thin Co-Ni-Re-WP single layer comparative material is slightly improved after annealing for Ms, Mr, Hc, and S, whereas the thick single layer comparative material is the same temperature It was observed that Mr, Hc, and S were significantly reduced after annealing. This is accompanied by a narrowing of the out-of-plane hysteresis curve shown as the MH plot in FIG. Here, M is the out-of-plane absolute magnetization of the material, and H is the strength of the magnetic field applied from an external source. In contrast, such a sharp narrowing of the hysteresis curve after annealing was not observed in the thin single layer comparative material. This is apparent from the MH curve shown in FIG. The same is true for the multilayer material 20, as shown in the MH curve of FIG. In other words, the multilayer material maintained a much higher Mr, Hc, and S after annealing than did the thick single layer comparative material. This different thermal behavior is believed to be related to the thickness of the Co—Ni—Re—WP film. As shown in FIG. 7, the magnetic characteristics deteriorated by annealing when the film thickness was approximately 5.1 μm. On the other hand, as shown in FIG. 6, when the film thickness was about 1.4 μm, the magnetic characteristics were not deteriorated and slightly improved. Therefore, thermal degradation of magnetic properties can be avoided by keeping each Co—Ni—Re—WP layer of the multilayer material as thin as approximately 1 μm as shown in FIGS.

  Comparing the annealed magnetic properties of the ML1 material containing the electroplated Cu layer with the annealed magnetic properties of the ML2 material containing the electrolessly plated (chemically plated) Cu layer, the ML2 material is more hot. Stability. Although the Mr and Hc of the ML1 material with the electroplated Cu layer are slightly reduced, their properties of the ML2 material with the electrolessly plated (chemically plated) Cu layer are slightly improved. These differences are caused by the difference in the thickness of the Cu layer of the ML material formed by electrolytic plating and the thickness of the Cu layer of the ML2 material formed by electroless plating (chemical plating). This difference in layer thickness is apparent from the SEM images shown in FIGS. The duration of the electroplating used to form the ML1 material Cu film is the same as the duration of the electroless plating of the ML2 material Cu film (60 seconds), but the electroless deposition of Cu is very slow, This results in a very thin Cu film. Therefore, better thermal stability than that obtained by electrolytic deposition can be obtained.

  In other embodiments of the present invention, it is anticipated that a non-magnetizable, electrically conductive layer of Au can be substituted for the Cu film of the first embodiment described above.

  In a further embodiment of the invention, alternating multilayer materials (not shown) are provided. The alternating multilayer material is substantially the same as that described above with reference to FIG. 1, except that a magnetizable Co—Pt—P film is used instead of a magnetizable Co—Ni—Re—WP film. The difference is that a non-magnetizable Au film is used instead of a non-magnetizable Cu film. Au is used for this alternate material as a non-magnetizable film between magnetizable Co-Pt-P films, but the above mentioned regarding electroplating or electroless plating (chemical plating) of non-magnetic films The observation applies equally to the alternate material of this other embodiment. It is contemplated that the Co-Pt-P material may be the material of construction and manufacture described in Singapore Patent Application 200500445-2.

FIG. 1 is a schematic cross-sectional view of a multilayer material that specifically represents the present invention. FIG. 2 is a graph showing the film thickness of the deposited Co—Ni—Re—WP layer material with respect to the time of the electroplating operation to form the Co—Ni—Re—WP layer. is there. FIG. 3 shows the hysteresis curve of a thick single layer comparative material, which plots the out-of-plane displacement of the material's absolute magnetization against the displacement of the magnetic field strength applied from an external source. FIG. 4 shows a hysteresis curve of a thin single layer comparative material, which plots the same variables as those shown in FIG. FIG. 5 shows the hysteresis curves of two multilayer materials that specifically represent the present invention, which is a plot of the same variables as those of FIGS. FIG. 6 is a reproduction of a scanning electron microscope image showing a cross section of a thin single layer comparative material. FIG. 7 is a reproduction of a scanning electron microscope image showing a cross section of a thick single layer comparative material. FIG. 8 is a reproduction of a scanning electron microscope image showing a cross section of a multilayer material in which a non-magnetizable layer has been deposited by electroplating. FIG. 9 is a reproduction of an image of a scanning electron microscope showing a cross section of a multilayer material in which a non-magnetizable layer is deposited by electroless plating (chemical plating).

Claims (14)

A multilayer material used in a microelectromechanical system (MEMS) device, wherein the multilayer material is a magnetizable material comprising cobalt, nickel, rhenium, tungsten, and phosphorus (Co—Ni—Re—WP). A multilayer material comprising a plurality of layers, each adjacent or each set of Co—Ni—Re—WP layers having each layer of non-magnetizable electrically conductive material therebetween. The multilayer material according to claim 1, wherein the non-magnetizable electrically conductive material between the adjacent Co-Ni-Re-WP layer pairs is copper (Cu). The multilayer material has at least five layers of magnetizable material, each of which is separated from the adjacent layers of magnetizable material by each layer of non-magnetizable electrically conductive material therebetween. The multilayer material according to claim 1 or 2 . The multi-layer material includes a base layer of the or another non-magnetizable electrically conductive material, the base layer acting as a seed layer that bonds the remainder of the multi-layer material to a substrate . 4. The multilayer material according to any one of 3 . It said layer of magnetizable material, a multilayer material according to any one of claims 1 to 4, each having a thickness in the range of 0.1-2 .mu.m. The layers of the non-magnetizable electrically conductive material disposed between adjacent sets of layers of the magnetizable material each have a thickness in the range of 0.1 μm to 0.5 μm . The multilayer material according to any one of 5 . Microelectromechanical systems (MEMS) device including a multilayer material according to any one of claims 1 to 6. A multilayer material used in a microelectromechanical system (MEMS) device, the multilayer material comprising a plurality of layers of magnetizable material, wherein a set of adjacent layers of the or each magnetizable material is in between having each layer of non-magnetizable electrically conducting material, at least a layer of said magnetizable material, Ri thickness der ranging 0.1-2 .mu.m,
The magnetizable material is a multilayer material comprising cobalt, nickel, rhenium, tungsten, and phosphorus (Co—Ni—Re—WP) . The multilayer material according to claim 8 , wherein the layer of magnetizable material has a thickness in the range of 0.5 μm to 1.5 μm. A method of manufacturing a multilayer material used in a microelectromechanical system (MEMS) device, the method comprising: a plurality of layers of magnetizable material and a plurality of layers of non-magnetizable electrically conductive material Forming different layers on top of each other such that adjacent sets of layers of said or each magnetizable material have each layer of non-magnetizable electrically conductive material therebetween. See
The method of manufacturing a multilayer material, wherein the layer of magnetizable material includes cobalt, nickel, rhenium, tungsten, and phosphorus (Co—Ni—Re—WP) . The method for producing a multilayer material according to claim 10 , comprising a step of forming the layer of the magnetizable material by electrolytic plating. The method for producing a multilayer material according to claim 10 , comprising a step of forming the non-magnetizable layer of the electrically conductive material by electroless plating. Placing the substrate on which the layer of magnetizable material and the non-magnetizable layer of electrically conductive material are formed in an electrochemical bath, thereby forming the layers on the substrate. The manufacturing method of the multilayer material in any one of 10-12 . The method for producing a multilayer material according to claim 10 , wherein the layers of the magnetizable material are each formed to a thickness in the range of 0.1 to 2 μm.