Patent Application
20120280393
The invention relates to a microelectromechanical system. Furthermore, the invention relates to an integrated circuit with a microelectromechanical system of this type and a method for producing an integrated circuit.
A microelectromechanical system by applicant is known e.g. from WO 2009/003958.
An electromechanical microswitch as described in U.S. Pat. No. 6,529,093 can be used for switching a radio frequency signal, in particular in GHz range. In particular for microelectronic circuits which are timed with very high frequencies in the GHz range, it is very helpful to have electromechanical microswitches which facilitate switching electrical connections on and off in a controlled manner. In U.S. Pat. No. 6,529,093 recited supra, a micromechanical switch is described which is made from a cantilever made from polysilicon and which is driven by an electrode arrangement to which an electrical potential is applied. Besides the electrode arrangement for driving the cantilever, a second electrode arrangement is provided therein for switching the RF signal. At least one of the electrodes of an electrode pair is thus provided with a dielectrical layer. The cantilever can thus also be configured as a bridge that is clamped on both sides. The layer configuration required for implementing the microswitch thus includes partially applied layers made from a dielectric material, conductors and polysilicon. Also in U.S. Pat. No. 6,639,488 a microswitch is described whose layer configuration is characterized by applying various dielectric and electrically conductive layers. Though in both documents production methods are used which are designated as CMOS compatible, they require method steps for producing the microswitches which are not required for producing microelectronic circuits.
In particular in circuits which are produced through the CMOS technology that is typically used in the semiconductor industry and which circuits are being used in wireless data transmissions and communications, typically electromechanical switches are being used which cannot be integrated together with electronic circuits on one chip. It would be much more cost-effective and advantageous in order to achieve further miniaturization to provide an electromechanical microswitch which is furthermore provided in a CMOS compatible manner so that an electromechanical microswitch can simultaneously be produced with the microelectronic circuit.
In view of this fact, it is important to generally understand the CMOS production process which is divided into a front-end of line (FEoL) portion and a back-end of line (BEoL) portion. While the process steps of the FEoL portion relate to producing the transistors directly on the surface of the silicon substrate, the transistors are connected with one another through electrical conductors in the BEoL portion. In particular, such connections are produced from the structuring of horizontal metal planes and vertical conductors (so-called Vias) which are embedded into electrically insulating layers between the horizontal metal planes. Thus, the processes performed in the two portions FEoL and BEoL differ substantially with respect to their thermal budget, in particular with respect to the level and duration of the process temperatures used. Thus, very high process temperatures occur in the FEoL portion, which are not reached again in the BEoL portion in order not to destroy the complex transistor build ups through the inter-diffusion processes.
As described supra, the recited solutions implement an electromechanical microswitch based on silicon, wherein the microswitch has to be produced through FEoL processes. From a process technology point of view, producing an electromechanical microswitch in the BEoL portion is much more advantageous.
U.S. Pat. No. 6,667,245 describes a method for producing a MEMS-RF switch in which Vias are being used as structural elements of a switch in the BEoL process.
Based on this, it is an object of the invention to provide a device for switching an electrical signal and a method for producing the device which are configured so that a production can be provided CMOS process compatible in the BEoL portion. In particular, the device shall be configured for switching signals, in particular radio frequency signals in the GHz range.
With respect to the device, the object of the invention is achieved through a microelectromechanical system (MEMS) with an electromechanical microswitch for switching an electrical signal, in particular a radio frequency signal (RFMEMS), in particular in GHz range, the electromechanical system including:
The microelectromechanical system (MEMS) is configured in particular for switching an electrical signal configured as a radiofrequency signal as a radio frequency microelectromechanical system (RFMEMS) in particular for switching high frequency signals in the GHz range.
The invention also relates to an integration of an electronic circuit with a microelectromechanical system, wherein the electrical circuit is preferably configured as an integrated CMOS circuit in order to achieve the object of the invention.
The object is achieved through the method recited supra, wherein the integrated circuit is produced through a CMOS method including the following steps:
The invention is based on the idea that approaches used so far to implement a micromechanical switch based on silicon or made from solid silicon material are not suitable to configure a micorelectromechanical switch in a CMOS compatible manner in a BEoL portion. The inventors have found that it is possible to advantageously integrate an electromechanical microswitch in a BEoL portion through a suitable choice of microswitch materials using the layer sequence used for connecting the electromechanical components. The inventors have also found that it is feasible through the process technologies that have become available in recent years to integrate or implement suitable electromechanical microswitches in microelectromechanical systems as it is known in principle e.g. from WO 2009/003958. Thus, electromechanical system technologies of the applicant have related to developing mechanically movable structures from solid material, in particular from silicon wafers.
Using a layer sequence for configuring the electromechanical microswitch according to the invention leads to an advantageous configuration of the particular functional elements of the electromechanical microswitch, thus e.g. the contact pivot, the opposite contact and the drive electrodes for the contact. The contact pivot is advantageously elastically movable and configured conductive. The opposite contact is advantageously configured at a distance from the contact pivot, in particular in the form of a solid and rigid opposite contact pedestal.
The microswitch within the microelectromechanical system is advantageously produced so that the contact pivot is movable through one or plural provided drive electrodes which can be arranged below or above the contact pivot with reference to the surface e.g. of the silicon substrate. This is provided by applying an electrical potential between the at least one drive electrode and the contact pivot so that an elastic movement of the contact pivot is performed as a function of the electrostatic forces and the capacitive coupling is changed through the contact between the opposite contact and the contact pivot. This causes a switching of the electrical signal which can be run on the opposite contact and/or the contact pivot. Advantageously, the contact pivot can be connected to ground and the opposite contact can be run between different potentials, for a decreasing distance between the contact pivot and the opposite contact, thus a capacitive coupling of the signal conduction with ground is provided.
An embodiment of the invention advantageously provides a combination of two measures which have additionally proven particularly advantageous for the function of the electromechanical microswitch. On the one hand side, it can be provided that the opposite contact (pedestal) includes a metal-insulator-metal (MIM) structure at a distal end oriented towards the contact pivot (actuator). This embodiment facilitates using an MIM structure of this type among other things for protecting the opposite contact and also for improving the contact performance, possibly expanding the frequency range. Thus, in particular the switching properties of the electromechanical microswitch can be advantageously configured.
It can furthermore be provided that the drive electrode (configured as a portion of a conductive layer of the conductive path layer stack) moving the contact pivot includes a structure including knobs with dielectric material on a side oriented towards the contact pivot. These knobs as implemented in the embodiment can be produced within a process step for exposing an electrode of a conductive path without requiring a separate process step for implementing the knob structure. As a matter of principle, the knob structure is advantageously configured to prevent unintentional contacting between the drive electrode and the contact pivot, thus an undesired short circuit. Additionally, the knobs are configured to support the drive electrode in the portion of the drive electrode or to implement a stop for the contact pivot. This process step for producing the knobs can be provided e.g. during a wet etching step and optionally during a subsequent CO2 drying process. Additional process steps for implementing the knob structure are not required. With respect to the structure including knobs made from dielectric material, it has proven particularly advantageous in the context of the production method that the dielectric material is formed as an oxide of a material of a conductive path of the multi-layer conductive path stack, in particular through wet chemical etching.
Additional advantageous embodiments of the invention can be derived from the dependent claims and provide advantageous embodiments to implement the concept described supra to achieve the object and to achieve the recited and additional advantages.
It has proven particularly advantageous that the contact pivot is configured as a cantilever, e.g. in the form of a unilateral spring or bridge. A bridge or spring (cantilever) can be provided e.g. with comparatively well-configured elastic properties in order to advantageously configure the elastic movement of the contact pivot for switching the signal. For this purpose, the contact pivot can be provided with recesses. In particular, the contact pivot for integrating the electromechanical microswitch can be provided with an electronic circuit on a chip through structuring a conductive level of the multi-level conductive path layer stack with one or plural end side fixation supports. A fixation support is configured for example as an outrigger of the contact pivot. Thus, it is advantageous to arrange the outriggers at an angle relative to one another that is different from 0° or 180° degrees in order to lock degrees of freedom of the movement of the contact pivot and in order to allow only one movement in switching direction. Two respective end side outriggers of the contact pivot have proven advantageous for forming fixation supports which are arranged at an angle of approximately 90° relative to one another.
In a particularly advantageous manner, the contact pivot includes at least one attractive portion that can be differentiated from the contact zone. The contact zone is thus associated with the opposite contact and is used for capacitive coupling of contact pivot and opposite contact. The at least one attractive portion, however, is associated with the activating drive electrode and is used for activation, that means force impact onto the contact pivot in order to set the contact pivot in motion.
The contact pivot is advantageously formed by structuring a conductive level of the multi-level conductive path stack and is preferably made from metal material, e.g. aluminum. Implementing the contact pivot from a metal conductive path of the multi-level conductive path stack can be advantageously integrated into the BEoL process.
As a matter of principle, one or more drive electrodes can be provided that activate the contact pivot and/or activate the contact pivot in another direction, wherein the drive electrodes are advantageously configured from the structuring of a conductive level of the multi-level conductive path stack. For example, a particularly advantageous embodiment can include a drive electrode that activates the contact pivot, wherein the drive electrode is arranged below the contact pivot with respect to the surface of the silicon substrate. This embodiment causes the contact pivot to be moved into a “down condition” for closing the switch and into an “up condition” for opening the switch. For improving the switching properties, additionally or alternatively, another drive electrode which activates and/or counter-activates the contact pivot can be arranged at a distance with respect to the surface of the silicon substrate above the contact pivot. In case the drive electrode that is oriented away from the substrate and arranged above the contact pivot is provided in addition to the lower substrate side drive electrode, the upper drive electrode is used as a pullback electrode. Thus, the movement of the contact pivot from the “down condition” into the “up condition” can be accelerated.
In a preferred manner, various conductive levels of the multi-level conductive path layer stack e.g. made from aluminum are simultaneously configured as carrier layers for the contact pivot, the opposite contact, the activating and/or counter-activating drive electrodes of the electromechanical microswitch. In a particularly preferred manner, the metal conductive levels can be coated at least on one side, preferably on both sides. In a particularly preferred embodiment, this applies for all metal conductive levels forming the electromechanical microswitch at least in the portion of the contact, the opposite contact, the activating drive electrode and the counter-activating drive electrode. The coating is presently advantageously formed by one or plural layers with TiN and/or Ti and/or AlCu. In particular a double layer from TiN—Ti has proven advantageous or a sandwich made from TiN—AlCu—TiN.
In a preferred embodiment, the base of the opposite contact is formed from insulating material. It has become apparent that when producing the multi-level conductive path layer stack, the insulating material arranged between the conductive levels, for example a dielectric material, preferably Si3N4 can also be advantageously used for forming the base of the opposite contact. In a particularly advantageous manner, the base of the opposite contact is formed from a sequence of a first metal conductive level, an insulating material placed thereon and a second metal conductive level.
The metal layer of the opposite contact has particularly advantageous switching properties with respect to the contact with the contact surface of the contact pivot.
Furthermore, applying an MIM structure (metal-insulator-metal structure) on a base for forming a distal end of the opposite contact is advantageous. Thus, it has proven advantageous in particular that the MIM structure includes:
The barrier layer is advantageously used as a protection between a metal layer that is applied to the base of the opposite contact and conducts a signal, and the dielectric layer of the MIM structure. The cap of the MIM structure is advantageously used for protecting the opposite contact. Advantageously, as a variation of this embodiment, the cap is provided with a higher layer thickness than the barrier layer. This facilitates that in a “down condition” of the contact, a reliably defined and comparatively low capacity is implemented. In order to further improve contact properties, the conductive cap, in particular the metal cap, can also be provided in the form of a metal layer structure which can be implemented as required. The barrier layer can advantageously be of the same type as the cap. The insulating dielectric layer of the MIM structure is advantageously made from Si3N4.
In a particularly preferred manner, the contact pivot and/or the cap can be formed from a metal conductive layer or from a layer combination which includes material based on titanium nitrite and/or titanium, in particular from a titanium nitrite material or pure titanium. In particular, in a “down condition” of the electromechanical microswitch, a titanium nitrite-titanium nitrite (TiN—TiN) contact or a TiN—Ti contact have proven comparatively wear resistant.
Thus, the contact pivot and/or the cap can be formed from one or plural layers Ti, TiN, and/or AlCu. These material combinations have proven to be easily processable, extremely wear resistant in a “down condition” and advantageous with respect to the shifting properties. A sandwich structure made from TiN—AlCu—TiN has proven particularly advantageous for implementing the contact pivot and the cap. Thus, it is advantageous that the entire conductive levels of the conductive path layer stack are configured in this sandwich structure, thus also in the portions where structured conductive levels are used for electrically connecting electronic circuits.
In another preferred embodiment, a distance of a conductor arrangement (drive electrode) activating the contact pivot from the contact is selected greater than a distance of the contact pivot from the opposite contact. Put differently, a distance between the opposite contact and the contact is smaller than a distance between a drive electrode and the contact pivot. Thus a “pull in effect”, this means an over-rotation of the contact pivot from the “up condition” into the “down condition” when closing the switch is advantageously counteracted.
In a particularly preferred embodiment, the distance between the opposite contact and the contact zone of the contact pivot and the capacity of the MIM structure on the opposite contact can be sized so that over the entire distance during the movement of the contact between an “up condition” and a “down condition”, a substantially proportional capacity diagram is achieved as a function of the activation voltage between the drive electrode and the contact pivot. The electromechanical microswitch is advantageously usable in one embodiment as a variable capacity with a defined control voltage diagram.
Embodiments of the invention are subsequently described based on the drawing figure. The drawing figure does not necessarily illustrate embodiments to scale; rather the drawing is provided schematically or slightly distorted where this improves understanding. With respect to supplementation of the teachings that are directly apparent from the drawing figures, pertinent prior art is incorporated by reference. Thus it is appreciated that many modifications and changes with respect to the shape and the detail of an embodiment can be provided without deviating from the general concept of the invention. The features of the invention disclosed in the drawing and in the claims can be implemented in advantageous embodiments of the invention by themselves and also in any combination. Furthermore, all combinations of at least two features disclosed in the description, the drawing and/or in the claims are within the scope of the invention. The general idea of the invention is not limited to the exact shape or the detail of the subsequently illustrated and described advantageous embodiment or limited to an object which is narrowed compared to the object claimed in the patent claims. In disclosed ranges, also the values disposed within the recited ranges shall be disclosed as threshold values and shall be usable and claimable at will. For simplicity reasons, identical or like elements or elements with identical or like function are used with identical reference numerals.
Other advantages, features and details of the invention can be derived from the subsequent description of the preferred embodiments or from the drawing figure, wherein:
The microswitch illustrated in
Thus,
The electromechanical microswitch 1 illustrated in
When applying an electrical potential between the drive electrode 30 and the contact pivot 10, the contact pivot 10 is caused to perform an elastic movement which changes a capacitive coupling of the contact zone 13 of the contact pivot 10 with the opposite contact 20 and is thus configured to switch and electrical signal S in the conductive path 112.
As apparent from
As a block diagram,
In order to facilitate an elastic movement of the contact pivot 10 in a preferred dynamic range, the contact pivot 10 as evident from
The preferred configuration of the contact pivot 10 that is schematically evident from
The drive electrode 30 is formed in each of its portions 31, 32 through structuring the conductive plane M1 which in this embodiment is also formed from aluminum and a cover layer 39 also made from titanium nitrate.
The opposite contact 20 presently includes a base 21 made from a layer of non-conductive or insulating material Si3N4. Onto the base 21, additional layers are applied through forming the conductive path M2 according to the contour of the opposite contact 20, since the conductive path M2 in turn is made from a sandwich structure of an aluminum carrier layer with intermediary layers 22, for example made from TiN applied on both sides. On the surface of the distal end 23 of the opposite contact 20, a sequence of initially one barrier layer 24 oriented towards the base and made from conductive material presently metallic TiN is applied and thereon a dielectric layer 25 and eventually a conductive cap 26 oriented towards the contact pivot 10. The MIM sequence of conductive layer 24, dielectric layer 25 and conductive cap 26 is presently configured as a particular protection of the opposite contact 20 for improving the contact properties to the contact 10 and for configuring a defined switching capability. Presently, the protective conductive cap 26 is formed from a thin metal layer made from TiN which is directly applied to the dielectric layer 25 through a respective structuring process. The cap 26 however in a modified embodiment not illustrated herein can also be made from a layer sequence of different metal materials. At least the surface which is formed by the cap 26 thus laterally reaches over the surface of the contact pivot 10 as apparent e.g. from
With reference to
It is appreciated that associating the contact pivot 10, the activating drive electrode 30 and the opposite contact 20 relative to the conductive planes M3, M1, M2 in the present embodiments is not to be interpreted as a limitation, but can be selected in a variable manner. Thus, for example, the opposite contact 20 can also be arranged in a M3 metal layer and the activating drive electrode 30 can also be arranged in a conductive level M2. As a matter of principle, however, also the contact pivot 10 with respect to the surface of the silicon substrate 101 can be arranged below an activating drive electrode or below an opposite contact. Such embodiments are presently not illustrated explicitly. Additionally, the association of the contact pivot 10, the opposite electrode 20 and the drive electrode 30 of the electromechanical microswitch 1 with respect to the conductive path M1 through M5 of the multi-level conductive path layer stack 102 must not be performed sequentially, it is rather also possible that additional metal layers arranged between the contacts have no direct function in the electromechanical microswitch.
The opposite contact 20 is presently initially configured as a pedestal with a base which includes a layer sequence corresponding initially to the conductive level Ml, thereon an insulating dielectric layer 21 and then the accordingly structured conductive level M2. Thus the uppermost TiN layer of the conductive level M2, with respect to the TiN substrate, simultaneously forms the lower end layer of the MIM structure, which is arranged on the opposite contact 20. The MIM structure additionally includes a dielectric layer 25 which includes, for example, TiN—Si3N4 and an additional TiN layer configured as a metal cap 26. The details of the MIM structure are illustrated in the enlarged detail of
a illustrates an electromechanical microswitch 1, which is provided with a structure 33, including knobs 34, on a side of the activating drive electrode 30 that is oriented towards the contact pivot 10, wherein the structure is illustrated in more detail in the blown up illustrations of
In summary, an electromechanical system (MEMS) 100, 200, including an electromechanical microswitch 1 for switching an electrical signal S in particular a radio frequency signal (RFMEMS) in particular in a GHz range has been described, including:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 047 599.0 | Dec 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/069019 | 12/7/2010 | WO | 00 | 7/12/2012 |
