Abstract:
To create a broad band spectrometer, a plurality of individual antenna based bolometers are fabricated on the surface of a single spectrometer chip, each bolometer having an individual antenna which is sized differently from all others, thus being responsive to a generally unique frequency of radiation. Each antenna is coupled to a related transistor, which is easily formed using CMOS technology. The antennas are connected to opposite sides of a transistor gate, thus creating a termination resistor for the particular antenna. Multiple outputs from the various antennas are then coupled, thus providing responsiveness to electromagnetic radiation of a very broad spectrum.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/774,087 entitled DETECTOR FOR DETECTING ELECTROMAGNETIC WAVES, filed Jul. 6, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a chip based spectrometer utilizing CMOS technology. More specifically, the present invention relates to a CMOS spectrometer made up of multiple antenna elements, with each antenna element operatively coupled to the gate of a corresponding CMOS transistor. 
       BACKGROUND OF THE INVENTION 
       [0003]    Detectors and sensors of all different types are utilized in virtually every walk of life. The miniaturization and efficiency of any sensor is a continuous goal for device designers. Stated alternatively, it is almost always beneficial to design and develop sensors and detectors which are more efficient and which can be packaged as smaller devices. By developing small efficiently operating sensors, various additional applications are typically made possible. This is specifically applicable to sensors which detect different types of radiation. 
         [0004]    One known method for detecting radiation is by means of optical detectors that convert a photon into an electron via electron/hole generation upon impact of a photon in a generation/recombination zone. The sum of the electrons/holes generated by the photons represents a signal current that corresponds to the received optical power. This is equivalent to the number of photons incident to the detector that are actually converted to electrons. The conversion is typically done in a photo diode. 
         [0005]    Another way of converting light involves treating the light signal as an electromagnetic wave and detecting via antennas or absorbing area. In an antenna coupled Bolometer, the energy of the electromagnetic wave received by the antenna is absorbed in a sensor element, which leads to an increase in temperature in the sensor element. The change in temperature causes a change in the electrical properties of the sensor element (e.g. a change in electrical resistance or change of the tunneling current in a semiconductor). 
         [0006]    Existing CMOS based sensors, which are effective for their given purposes, allows for the generation of the far-infrared bolometer. Far-infrared bolometers of many different types presently exist, however they are not efficiently designed for speed and responsiveness. 
         [0007]    Using a frequency selective antenna, a bolometer which responds to radiation of a particular frequency can be envisioned. That is, the bolometer is designed to detect a prescribed frequency of radiation, and then produce an appropriate output signal. Using an array of different sized antenna coupled bolometers, a wide frequency range can be covered. Typically, these revised devices are spectrometers, which are useful for many different applications. Spectrometers are typically utilized to detect wide band spectral characteristics. A spectrometer is particularly useful, and essential, for chemical analysis in many types of areas. 
         [0008]    As such, there is a need for compact spectrometers, which can easily be implemented in microelectronic chip format. Further, there is a need for a compact spectrometer which is efficient and responsive to a broad spectrum of radiation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention provides chip based spectrometers which are operable and sensitive across wide frequency ranges, thus useable for many different applications. The spectrometer makes use of multiple antennas, each configured to be responsive to a selected frequency or range of frequencies. All of these multiple antennas can be easily realized as part of a single chip, thus providing a very compact spectrometer. Further, due to the very small size of the necessary antennas, a large number of antennas may exist on the chip, thus providing a broad range of responsiveness. Each antenna can easily be positioned relative to a related CMOS transistor, resulting in the effective operation of the device as a broad band spectrometer. 
         [0010]    This device more specifically includes a number of antennas with each coupled to the gate of a corresponding transistor. This configuration provides a far infrared based spectrometer. When infrared radiation is presented to each antenna, this radiation is converted to electrical current. Two terminals of the antenna are connected to the two sides of a MOSFET gate. This way, the MOSFET gate resistance acts as the terminating resistor of the antenna. This antenna current is converted to heat at the transistor gate and changes the operating temperature, and the leakage characteristics of the transistor. By detecting these changes in operation, the above-referenced infrared radiation is detected as an electrical signal that can be utilized by subsequent devices. 
         [0011]    As outlined above, the incorporation of multiple antenna based bolometers allows for detecting a broader spectrum of IR radiation thus providing spectrometer capabilities. That said, each of these antennas are typically specifically designed and configured to detect IR radiation within a specific frequency range. This is primarily due to the geometry of the antenna itself which is sensitive to a particular frequency. By selecting a narrow band high Q antenna, it is possible to construct bolometers which are sensitive to a very focused frequency range. A large number of antennas with each having a slightly different mechanical dimension allows for the coverage of a large frequency range. 
         [0012]    As mentioned above, the broad band sensitivity necessary for spectrometers can often be challenging. The present invention addresses this challenge by providing wavelength accuracy due to the mechanical dimensions of each particular antenna. As the physical structure making up the antenna can be easily controlled on a silicon chip, accurate antennas are thus produced. Further, wavelength accuracy is often affected by dielectric properties of materials used in the back end of the line CMOS process (BEOL). However, in a spectrometer using a known substance and having known absorption lines, calibration can easily be performed. In addition, drift will thus affect all antennas similarly, and thus not have effects on the overall spectrometer operation. 
         [0013]    According to a first aspect of the present invention, there is presented a detector for detecting electromagnetic waves, including a plurality of antennas for receiving the electromagnetic waves, and a plurality of related semiconductor elements attached to each antenna (i.e., the gate of a corresponding transistor). A termination section of the semiconductor element establishes a termination resistor of the antenna, which causes the heating of a temperature-sensitive part of the semiconductor element. The semiconductor element is temperature-dependent in that its operation is dependent on the temperature of the temperature sensitive part. Lastly, a measurement unit for measuring the temperature-dependent characteristic of the semiconductor element is utilized. 
         [0014]    Each detector according to this aspect of the invention receives the electromagnetic waves by means of the antenna and converts the received electromagnetic radiation into heat by means of the termination section of the semiconductor element. The termination section functions as termination resistor of the antenna. The heat produced in the termination section is used for heating a temperature-sensitive part of the semiconductor device. The temperature-sensitive part can be any part of the semiconductor-element that comprises a measurable temperature-dependent characteristic. Advantageously, the termination section is arranged in the proximity of the temperature-sensitive part. Advantageously, the termination section heats the temperature-sensitive part selectively. In other words, the termination section does not heat the complete semiconductor element evenly or uniformly, but produces the heat at or in the proximity of the temperature sensitive part. In other words, the produced heat is focused on the area of the temperature sensitive part. Such a focusing of the heat on the temperature-sensitive part enhances the sensitivity of the detector. 
         [0015]    According to a further embodiment of this aspect of the invention the semiconductor element associated with each antenna is a transistor, wherein the termination section is established by means of an electrode of the transistor and wherein the respective electrode is coupled at two termination points to an arm of the antenna. 
         [0016]    According to this embodiment one of the electrodes of the transistor acts as termination resistor for the antenna. The respective electrode is coupled at two termination points to an arm of the antenna. The respective electrode comprises preferably a gap between the two termination points. In other words, the respective electrode comprises two parts, wherein each part is connected to one of the arms of the antenna. The termination section or termination resistor respectively can be established by using the semiconductor path between the two termination points or the two electrode parts respectively. The termination points are advantageously arranged at opposite sides of the transistor. This provides space for establishing the required matching impedance between the termination points via the semiconductor substrate. The transistor electrodes offer inexpensive contact possibilities for the antenna. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Further objects and advantages of the present invention will be seen by reading the following detailed description, in conjunction with the drawings in which: 
           [0018]      FIG. 1  shows a schematic illustration of a detector for detecting electromagnetic waves according to an embodiment of the present invention. 
           [0019]      FIG. 2  shows a schematic illustration of a circuit diagram of a detector according to an embodiment of the invention; 
           [0020]      FIG. 3  shows a schematic cross-section of an integrated circuit comprising an antenna and a semiconductor element of a detector according to an embodiment of the present invention; 
           [0021]      FIG. 4  shows the layout of a planar antenna of a detector according to an exemplary embodiment of the invention; 
           [0022]      FIG. 5  shows a 3-dimensional view of another detector according to an embodiment of the present invention comprising a bipolar transistor; 
           [0023]      FIG. 6   a  shows a top view of another detector according to an embodiment of the present invention comprising a diode; 
           [0024]      FIG. 6   b  shows a cross-section of the detector of  FIG. 6   a;    
           [0025]      FIG. 7  shows a schematic illustration of a thermal imaging device; 
           [0026]      FIG. 8  shows a top view of one embodiment of a spectrometer chip; 
           [0027]      FIG. 9  shows a top view of a second embodiment of the spectrometer chip of the present invention; and 
           [0028]      FIG. 10  is a spectral graph illustrating the spectral operation of the spectrometer. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIG. 1  shows a schematic illustration of a detector  100  for detecting electromagnetic waves  150  according to an embodiment of the present invention. The detector  100  is in particular suitable for detecting electromagnetic waves  150  with a frequency in the THz range. The detector  100  comprises an antenna  101  for receiving the electromagnetic waves  150 . The antenna  101  can be e.g. a planar broadband antenna with a ground plane. The antenna  101  is in particular suited to receive electromagnetic waves in a wavelength range between 3 μm and 15 μm. The antenna  101  comprises a first arm  102   a  and a second arm  102   b . The first arm  102   a  is connected by means of a first via  103   a  to a first termination point  104   a  and the second arm  102   b  is connected by means of a second via  103   b  to a second termination point  104   b . The first termination point  104   a  and the second termination point  104   b  are contact points for contacting a gate  106  of a Field Effect Transistor (FET)  105 . Thus the gate  106  of the FET  105  is connected on both sides of the FET  105  to the antenna  101 . The FET  105  is preferably a Metal Oxide Semiconductor (MOS)-FET or an Insulated Gate (IG)-FET respectively. The gate resistance between the first termination point  104   a  and the second termination point  104   b  acts as termination resistor for the antenna  101 . The value of the gate resistance is preferably designed in such a way that the antenna  101  is matched by means of the gate resistance. The source  107  of the FET  105  is coupled to ground potential. The drain  108  of the FET  105  is biased with a positive potential VDD. Between the drain  108  of the FET  105  and the positive potential VDD a measurement unit  109  for measuring a temperature-sensitive characteristic of the FET  105  is provided. According to this exemplary embodiment of the invention the measuring unit  109  is a current meter. 
         [0030]    The second arm  102   b  of the antenna  101  is coupled to a gate bias potential via a resistor  110 . The resistor  110  could be replaced by an inductor. The FET  105  is operated in sub-threshold mode, i.e. there are only leakage currents flowing. 
         [0031]    In operation, the detector  100  receives electromagnetic waves  150  via the antenna  101 . The electromagnetic energy received by the antenna  101  is converted to heat by means of the gate resistance of the gate  106 . This is in turn heating up the drain-source channel of the FET  105  which functions as the temperature-sensitive part of the detector  100 . This in turn affects and influences the sub-threshold gate leakage current as well as the sub-threshold drain-source leakage current of the FET  105  which can be used as a measurable temperature-dependent characteristic of the FET  105 . In the embodiment shown in  FIG. 1 , the temperature dependent drain-source leakage current is measured by means of the measurement unit  109 . 
         [0032]      FIG. 2  shows a circuit diagram of a readout circuit of a detector  200  according to an embodiment of the invention. The readout circuit comprises a sensor circuit  201 , a reference circuit  202 , a current mirror circuit  203  and an amplifier circuit  204 . The sensor circuit  201  comprises an antenna  205  as well as a Field-Effect-Transistor (FET)  206 . The FET  206  comprises a gate  207 , a source  208  and a drain  209 . The gate  207  and the source  208  are coupled to ground potential. The drain  209  is biased with a positive potential of, e.g., 1V. 
         [0033]    The antenna  205  comprises a first arm  210  and a second arm  211  as well as a first via  212  and a second via  213 . The FET  206  is a MOS-FET. The gate  207  of the FET  206  is connected at a first termination point  214  to the first via  212  and at a second termination point  215  to the second via  213 . 
         [0034]    The drain  209  is coupled to the current mirror circuit  203 . The current mirror circuit  203  comprises a transistor  220  and a transistor  221 . The current mirror circuit  203  mirrors the drain-source current of the FET  206  with, e.g., the factor 1:10. The current mirror circuit  203  performs effectively a subtraction of the current in the reference circuit  202  and the current in the sensor circuit  201  to reduce the required dynamic range of the rest of the readout electronic. 
         [0035]    The reference circuit  202  comprises several switchable reference transistors to tune the readout circuit. For example, the tuning can be such that the current of the reference circuit  202  is ten times higher than the current in the sensor circuit  201 . 
         [0036]    The amplifier circuit  204  amplifies the drain-source current of the FET  206 . 
         [0037]    The FET  206  is operated in sub-threshold mode, i.e. there are only leakage currents flowing. 
         [0038]    In operation, the detector  200  operates in the same manner as detector  100  discussed above. Specifically, detector  200  receives electromagnetic waves via the antenna  205 . The electromagnetic energy received by the antenna  205  is converted to heat by means of the gate resistance of the gate  207 . This is in turn heating up the drain-source channel of the FET  206  which functions as temperature-sensitive part of the detector  200 . This in turn affects and influences the drain-source leakage current of the FET  206  which is amplified by means of the amplifier circuit  204  and can then be measured by a further not shown measurement unit. 
         [0039]      FIG. 3  shows a schematic cross-section of the sensor circuit  201  as shown in  FIG. 2 . The sensor circuit  201  is implemented as integrated circuit. It comprises the antenna  205  and the FET  206 . The first arm  210  and the second arm  211  of the antenna  205  are arranged in one common plane on the surface of the sensor circuit  201 . The first via  212  and the second via  213  extend orthogonal to the first arm  210  and the second arm  211 . Below the gate electrode  207  an insulating layer  308  of e.g. gate oxide is arranged. The FET  206  comprises a first n-doted layer  301 , a second n-doted layer  302  and in the middle a p-doted layer  303 . In other words, the FET  206  is an N-channel MOS-FET. The first n-doted layer  301  is connected to a not shown source-electrode and the second n-doted layer  302  is connected to a not shown drain-electrode. The antenna  205  is a planar antenna that is arranged on a dielectric substrate  304 . Next to the first n-doted layer  301  and next to the second n-doted layer  302  are arranged insulating oxide layers  305 . The integrated circuit of the sensor circuit  201  comprises further a buried oxide (BOX) layer  306  and a Silicon layer  307 . The antenna  205  is provided for receiving electromagnetic waves  350 . 
         [0040]      FIG. 4  shows a exemplary embodiment of a top view of the layout of the antenna  205  of  FIG. 2  and  FIG. 3  in more detail. It is a logarithmically periodic antenna that is designed for a wavelength range of 5 μm to 24 μm. 
         [0041]      FIG. 5  shows a 3-dimensional view of a detector  500  according to another embodiment of the present invention. The detector  500  is manufactured in SOI-technology. The detector  500  comprises an antenna  501  and a semiconductor element as a transistor  502 . The antenna  501  comprises a first arm  504  and a second arm  505  as well as a first via  506  and a second via  507 . The transistor  502  is a bipolar transistor and comprises two base electrodes  508   a  and  508   b , an emitter electrode  509  and a collector electrode  510 . 
         [0042]    The emitter electrode  509  is connected at a first termination point or termination area  511  to the first via  506  and at a second termination point or termination area  512  to the second via  507 . 
         [0043]    The two base electrodes  508   a  and  508   b  are coupled to a base layer  513 , the emitter electrode  509  to an emitter layer  514  and the collector electrode  510  to a collector layer  515 . 
         [0044]    Below the collector layer  515  there is arranged an insulating layer  516  of Silicon-Dioxide or of another thermally insulating material. Below the insulating layer  516  there is provided a base layer  517  of a semiconductor material, in particular Silicon. 
         [0045]    The antenna  501  is schematically illustrated as dipole antenna. It can generally be any antenna that is suitable for the required frequency range. It can be e.g. implemented as planar antenna as well, e.g. by means of a planar antenna as shown in  FIG. 4 . In case of a planar antenna the antenna  501  would be embedded in a not shown layer of dielectric material. 
         [0046]    In this embodiment the bipolar transistor  502  of the detector is operated in a forward-biased mode. In operation, a substantially constant base-emitter voltage is applied to the two base electrodes  508   a  and  508   b  and the emitter electrode  509 . The emitter electrode  509  acts as termination resistor for the antenna  501 . The emitter electrode  509  is designed in such a way that the electrical resistance between the first termination point  511  and the second termination point  512  corresponds to the matching impedance of the antenna. The electrical resistance will preferably be established by means of the emitter layer  514 . 
         [0047]    Preferably the emitter electrode  509  comprises a gap  518  between the first termination point  511  and the second termination point  512 . 
         [0048]    The electromagnetic radiation received by the antenna  501  is converted to heat by means of the electrical resistance between the first termination point  511  and the second termination point  512  of the emitter electrode  509 . This is in turn heating up the base layer  513  and the collector layer  515  of the bipolar transistor  502 . This in turn affects and influences the collector current which can be measured at the collector electrode  510 . The collector current is measured by means of a measuring unit  519 . The measuring unit  519  is implemented as current meter. 
         [0049]    In this embodiment of the invention the collector current is used as the measurable temperature-dependent characteristic of the bipolar transistor  502 . 
         [0050]    As a further embodiment, the antenna  501  could be terminated by means of the two base electrodes  508   a  and  508   b . Then the resistance between the two base electrodes  508   a  and  508   b  (the resistance of the base layer  513 ) would establish the termination resistor for the antenna  501 . 
         [0051]    According to a further embodiment of the invention the bipolar transistor  502  can be operated in the sub-threshold area, i.e. in a reverse-biasing mode. In this embodiment the sub-threshold base leakage current in the base layer  513  or the sub-threshold collector-emitter leakage current in the emitter layer  514  or the collector layer  515  can be used as measurable temperature-dependent characteristic of the bipolar-transistor  502 . 
         [0052]      FIG. 6   a  shows a top view of a detector  600  according to a further embodiment of the invention. The detector  600  comprises an antenna  601  and as the semiconductor element a diode  602 . The antenna  601  comprises a first arm  604  and a second arm  605 . The diode  602  comprises an n-doted layer  606  and a p-doted layer  607 . The n-doted layer  606  comprises two electrodes or electrode parts  608   a  and  608   b . The first arm  604  of the antenna  601  is connected at a first termination point  609   a  to the electrode  608   a  and the second arm  605  at a second termination point  609   b  to the second electrode  608   b.    
         [0053]    The diode  602  is operated in a forward-biased mode. This is established by applying a positive voltage V D  to the p-doted layer  607 . 
         [0054]    The resistance between the electrodes  608   a  and  608   b  functions as matching impedance for the antenna  601 . The electromagnetic radiation received by the antenna  601  is converted to heat right between these electrodes. This heats up the depletion layer between the n-doted layer  606  and the p-doted layer  607 . This in turn affects and influences the forward current of the diode  602  which is measured as temperature-dependent characteristic by means of a current meter  610 . 
         [0055]      FIG. 6   b  shows a cross section of the diode  602 . Next to the n-doted layer  606  and the p-doted layer  607  there are arranged thermally insulating layers  611  and  612  of Silicon-Dioxide or of another thermally insulating material. Below the layers  606 ,  607 ,  611  and  612  there is provided another thermally insulating layer  613  of Silicon-Dioxide or of another thermally insulating material. Below the layer  613  there is provided a base layer  614  of a semiconductor material, in particular Silicon. 
         [0056]      FIG. 7  shows a schematic illustration of a thermal imaging device  700  according to an embodiment of the invention. The thermal imaging device  700  comprises a lens  701  for focusing the electromagnetic waves  702  on a detector array  703 . The detector array  703  comprises several detectors  704  arranged in rows and columns for detecting the electromagnetic waves  702 . The lens  701  can be made movable, so that the incident electromagnetic waves (radiation)  702  can be focused on a single row of the detector array  703  or even on a single detector  704 . This corresponds to a scanning imaging device. 
         [0057]    The thermal imaging device  700  comprises a processing unit  705  for processing detector signals received from the detectors  704 . The processed detector signals are forwarded to a display  706  that is provided for displaying thermal images of the received electromagnetic waves  702 . 
         [0058]    Utilizing the bolometer technology outlined above, the present invention can provide a broad frequency spectrometer, capable of detecting radiation across a broad range of frequencies. Referring now to  FIG. 8 , a top schematic view of such a device is illustrated. More specifically,  FIG. 8  illustrates the top view of a first spectrometer chip  800  having a plurality of antenna elements all placed upon the surface thereof. As shown in  FIG. 8 , first spectrometer chip  800  includes a first antenna through eighth antenna ( 810 ,  812 ,  814 ,  816 ,  818 ,  820 ,  822  and  824 , respectively). As can be seen, each of these antennas are linear in nature and sized slightly differently, thus causing each antenna to be sensitive to different frequencies of radiation. Each antenna is electrically coupled to a related sensor. As shown, first antenna  810  is electrically coupled to first sensor  830 , second antenna  812  is electrically coupled to a second sensor  832 , etc. In this particular embodiment, first through eighth sensors ( 830 ,  832 ,  834 ,  836 ,  838 ,  840 ,  842 ,  844  and  846 ) are utilized to read signals detected by the related antenna. By providing an appropriate number of antennas and related sensors, a very broad spectrum of sensitivity can easily be achieved. The present invention generally contemplates the possibility of many more antennas than illustrated in  FIG. 8 . For example, it is entirely possible to fabricate first spectrometer chip  800  having as many as two hundred (200) antennas on a surface thereof. It is also contemplated that the spectrometer would effectively operate for the mm and sub mm (THz) frequency range. This broad range of operation in a compact package provides many advantages. While the actual management and connections for these multiple antennas may be somewhat challenging, the ability to fabricate such antennas using CMOS chip manufacturing techniques can be easily undertaken. 
         [0059]    As an alternative,  FIG. 9  illustrates a similar second spectrometer chip  900  having first through fourth circular antennas ( 910 ,  912 ,  914  and  916 , respectively) configured on the surface thereof. Again, each antenna is sized slightly differently to respond to signals of different frequencies. Further, second spectrometer chip  900  includes first through fourth sensors ( 930 ,  932 ,  934  and  936 ) each coupled to a corresponding antenna. Again, each sensor will provide the ability to detect signals generated by the respective antennas, thus allowing for the detection of radiation of differing frequencies. 
         [0060]    Although not shown, first spectrometer chip  800  and second spectrometer chip  900  also include connections to further components. For example, first through eighth sensors ( 810 ,  812 ,  814 ,  816 ,  818 ,  820 ,  822  and  824 ) may each be connected to an appropriate communication bus, thus allowing their outputs to be passed along to other devices. 
         [0061]    Referring now to  FIG. 10 , there is illustrated a simplified spectral graph illustrating the operation of the multiple antennas. Simply stated, each of the antennas are responsive to a defined frequency range, based upon their physical configuration. Spectral graph  1000  illustrates four different frequency response curves: first curve  1002 , second curve  1004 , third curve  1006  and fourth curve  1008 . As can be seen, each curve provides a peak centered around a particular frequency, f 1 , f 2 , f 3  and f 4 . Spectral graph  1000  can correlate with second spectrometer chip  900  in that it simply illustrates the frequency response of four different antennas. In this example, peak  1002  corresponds to first antenna  910 , peak  1004  corresponds to second antenna  912 , third peak  1006  corresponds to third antenna  914 , and fourth peak  1008  corresponds to fourth antenna  916 . When combined with another, the overall frequency response of spectrometer chip  900  allows for the detection and differentiation of radiation signals having different frequencies. Consequently, the above-discussed spectrometer operation is achieved. 
         [0062]    While first spectrometer chip  800  and second spectrometer chip  900  are illustrated above, it will be understood that many variations and adaptations of these designs could be easily utilized. The particular antenna design and the number of antennas will affect the overall operation. More specifically, each antenna may be designed to have its own desired bandwidth, which thus must cooperate with other antennas configured on the particular spectrometer chip. It is generally intended that each antenna will be configured as a relatively narrow band antenna, thus providing the ability to specify and differentiate particular frequencies. It is contemplated that various designs for the particular antenna utilized, and the collection of antennas as a whole, can be varied depending upon the design goals for the particular spectrometer chip. In addition, it is possible to configure the antennas to provide polarity information for the detected electromagnetic wave, should that information be valuable. 
         [0063]    Any disclosed embodiment may be combined with one or several of the other embodiments shown and/or described. This is also possible for one or more features of the embodiments. The present invention is further not intended to be limited to the embodiments shown, but rather is intended to include all modifications and variations coming within the scope and spirit of the following claims.