Abstract:
A micromechanical component and a corresponding test method for a micromechanical component are described. The micromechanical component includes at least one first region, which is elastically connected to a second region via a spring device, a resistor element, which is situated in and/or on the spring device and is at least partially interruptible in the event of damage to the spring device, and a detection device, which is electrically connected to the resistor element, for detecting an interruption in the resistor element and for generating a corresponding detection signal.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a micromechanical component and a corresponding test method for a micromechanical component. 
     BACKGROUND INFORMATION 
     The present invention and the problems on which it is based are explained here with respect to MEMS micromirror arrays, although, in principle, the present invention may be applied to any micromechanical components. 
     German Published Patent Application No. 10 2008 000 030 describes a manufacturing method for a micromechanical electrostatic adjusting device and a corresponding micromechanical electrostatic adjusting device, a mirror element being mounted via springs on a stationary region. 
     During operation or in the event of an overload, MEMS micromirrors may suffer damage in the form of cracks and/or breaks. If it cannot be detected promptly, such damage may cause safety-relevant problems for humans and machines. 
     To prevent such risks, it has been proposed that a monitoring method should be provided for detection of damage to such MEMS micromirror arrays. 
     For example, with MEMS micromirror arrays or with other MEMS structures, for example, actuators or sensors, optical monitoring units may be built into the overall module. The change in a beam of light reflected by the movable MEMS structure may be recorded by a photodiode. In the event of damage, signal changes in the photodiode are detected and transmitted to a monitoring ASIC. The ASIC then ensures an emergency cutoff or shutdown of a light source, for example, a laser light source. 
     If the micromechanical component includes a detection component in the form of a piezoresistive bridge circuit, the resistor element according to the present invention may be implemented by the fact that the detection component leads past a sensitive spot in the micromechanical component, which results in it being interrupted if damaged. In this case, the damage incident would be noticeable immediately due to loss of the detection signal, for example, the bridge output voltage. 
     SUMMARY 
     The idea on which the present invention is based involves the configuration of a resistor element in the form of an implanted piezoresistive resistor, for example, or an applied metallic resistor along a sensitive spring of a micromechanical component. 
     A metal resistor may be made of copper, aluminum or other metal alloys, for example. Also possible are a salicided resistor, a polysilicon conducting resistor or a resistor made of epitactically deposited polysilicon on the spring device of the micromechanical component. 
     In the event of damage such as breakage or cracking of the spring device, for example, the voltage applied to the resistor element or the current flowing through it undergoes a drastic change. The change in current or voltage may be picked up by an ammeter or a voltmeter. The corresponding detection signal may be relayed to an ASIC for triggering an emergency shutdown or for shutting down a light source. 
     One important advantage of using the resistor element according to the present invention in comparison with an essentially known analysis circuit, which analyzes the change in optical signals over time to infer a fault by analysis of a change in frequency components, for example, lies in the speed of detection of a break. Another advantage is the easy implementability in the overall process. 
     According to a preferred specific embodiment, the first region is a stationary region and the second region is an elastically deflectable mirror region. 
     According to another preferred specific embodiment, the first region is an elastically deflectable drive region and the second region is an elastically deflectable mirror region. 
     According to another preferred specific embodiment, the resistor element passes over the first region, so that it is interruptible even in the event of damage in the first region. This also permits continuous monitoring of the first region. 
     According to another preferred specific embodiment, the resistor element meanders over the first region. This increases the region for monitoring. 
     According to another preferred specific embodiment, the resistor element is connected to the detection device via the first region. 
     According to another preferred specific embodiment, the detection device is configured to detect the temperature via the resistor element. The resistor element may thus also be used simultaneously as a temperature sensor element integrated into the chip. In this case, the temperature coefficient is utilized for the temperature measurement. It should be pointed out that the temperature coefficient of an applied metal resistor is generally much lower than that of a diffused piezoresistive resistor. 
     According to another preferred specific embodiment, the detection device is configured to carry out a measurement of light intensity via the resistor element. The resistor element may thus at the same time also be used as a light sensor element integrated into the chip. The photo-effect of the doped semiconductor is utilized here. It should be pointed out that an applied metal resistor has no photo-effect. 
     According to another preferred specific embodiment, the spring device has a first section and a second section, the resistor element being formed in different ways in the first section and in the second section and being wired to the detection device in such a way that the detection device supplies a first detection signal when the resistor element is interrupted in the first section and supplies a second detection signal, which is different from the first detection signal, when the resistor element is interrupted in the second section. Local failure analyses or warnings may thus be output in this way. 
     According to another preferred specific embodiment, the detection device is designed for wireless transmission of the detection signal externally, in particular to a cell phone. A fault may be transmitted from the detection device wirelessly, for example, for display of the fault on an external display, for example, the display screen on a cell phone. Transmission of the fault by SMS or e-mail to the manufacturer to point out defects, risks or abuse is possible in order to carry out statistical analyses, if necessary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a first specific embodiment of the present invention. 
         FIG. 2  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a second specific embodiment of the present invention. 
         FIG. 3  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a third specific embodiment of the present invention. 
         FIG. 4  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a fourth specific embodiment of the present invention. 
         FIG. 5  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a fifth specific embodiment of the present invention. 
         FIG. 6  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a sixth specific embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The same reference numerals in the figures denote the same elements or those having the same function. 
       FIG. 1  is a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a first specific embodiment of the present invention. 
     Reference numeral  1  in  FIG. 1  denotes a micromechanical micromirror region, which is connected via springs  2   a ,  2   b  to a stationary region  100 , for example, a substrate region. Diffused into the material of regions  1 ,  100  and of springs  2   a ,  2   b , e.g., silicon, between nodes K 1  and K 2 , is a piezoresistive resistor R in the form of a narrow strip. 
     Nodes K 1 , K 2  are connected via printed electrical conductors I 1 , I 2  to an electrical detection device  50 . Detection device  50  includes a voltage source and an ammeter, for example, which are connected in series with printed conductors I 1 , I 2 . 
     In the event of a break or a partial break in springs  2   a ,  2   b , the amperage detected by the ammeter undergoes a significant change, whereupon a corresponding detection signal S may be generated. 
     Detection signal S may cause an emergency cutoff or shutdown of a laser source (not shown), for example, which is aimed at micromirror region  1 . 
     Wireless transmission externally to a smartphone or to some other cell phone for display of detection signal S, for example, is also possible. 
     A crack, i.e., a break, in micromirror region  1  may also be detected in the respective region since resistor element R is also guided over micromirror region  1 . 
       FIG. 2  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a second specific embodiment of the present invention. 
     In the second specific embodiment according to  FIG. 2 , two printed conductors are applied to nodes K 1 , K 2 , namely, printed conductors I 1 ′, I 1 ′ being applied to first node K 1 , and printed conductors I 2 ′, I 2 ″ being applied to second node K 2 . 
     Detection device  50 ′ in this case includes a current source, which supplies a current through resistor element R via printed conductors I 1 ′, I 2 ′. In addition, detection device  50 ′ includes a voltmeter, which measures a voltage drop across resistor element R via printed conductors I 1 ″ and I 2 ″. 
     In the event of a break or a crack in springs  2   a ,  2   b  or micromirror region  1 , detection signal S may be generated via the detected change in voltage. 
       FIG. 3  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a third specific embodiment of the present invention. 
     In the third specific embodiment according to  FIG. 3 , micromirror region  1  is connected to stationary region  100  at opposite sides via two parallel springs  2   a ′,  2   a ″ and  2   b ′,  2   b″.    
     In this case, resistor element R′ runs between nodes K 1 ′, K 2 ′, both of which are on the upper side of stationary region  100  shown in  FIG. 3 . 
     Resistor element R′ may be a diffused or sputtered resistor, for example, which runs from node K 1 ′ via spring  2   a ′ and micromirror region  1  to spring  2   b ′ and from there back via spring  2   b ′ and mirror region  1  to spring  2   b ″, after which it reverses direction and runs back via spring  2   b ″ and micromirror region  1  to spring  2   a ″ and from there to node K 2 ′. 
     As in the first specific embodiment, detection device  50  has a voltage source and an ammeter connected in series with it for generating detection signal S in the event of damage. 
       FIG. 4  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a fourth specific embodiment of the present invention. 
     In the fourth specific embodiment according to  FIG. 4 , in contrast with the first specific embodiment according to  FIG. 1 , a piezoresistive resistor R″, which has a meandering configuration in the region of the micromirror region, is provided, so that detection of a crack or break may also be accomplished by detection device  50  over a large surface in this region  1 . 
     The design is otherwise the same as that in the first specific embodiment. 
       FIG. 5  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a fifth specific embodiment of the present invention. 
     In the fifth specific embodiment according to  FIG. 5 , a first region  1   a , which functions as the drive region, and a second region  1   b , which functions as the micromirror region, are provided. 
     Drive region  1   a  is connected via springs  21 ,  26  to a stationary substrate region (not shown). Drive region  1   a  may be deflected with respect to the substrate region by a coil device, for example (not shown), which is provided thereon, and elastically restored via springs  21 ,  26 . Micromirror region  1   b  is connected to drive region  1   a  via a first section including springs  22 ,  23  and via a second section including springs  24 ,  25 . Micromirror region  1   b  may be deflected elastically by driver region  1   a  due to a resonant effect. 
     A piezoresistive resistor element R′ is formed, starting from a first node K 1 ″, via springs  26 ,  25 ,  24 , micromirror region  1   b  and springs  23 ,  22 ,  21 , leading to node K 2 ″. Nodes K 1 ″, K 2 ″ are connected to evaluation device  50  via printed conductors I 1 , I 2 , the evaluation device being formed as in the first exemplary embodiment described above. 
     Due to this configuration, a break in springs  21  through  26  or in micromirror region  1   b  is detectable by the evaluation device. 
       FIG. 6  shows a schematic cross-sectional diagram to illustrate a test method for a micromechanical component and a corresponding micromechanical component according to a sixth specific embodiment of the present invention. 
     In the sixth specific embodiment according to  FIG. 6 , a first resistor R 1  is formed between node K 2 ″ and node K 1 , sitting on micromirror region  1   b . A second resistor R 2 , which has a different resistance value than the resistance value for R 1 , is formed between node K 1 ″ and node KR. 
     A third resistor R 0 , which is connected to a ground potential M via a printed conductor I 3 , is formed in parallel to resistor R 2 , starting from node K 3 ″ and leading to node KR. 
     In this specific embodiment, a break or a crack in the region of the first section including springs  21 ,  22 ,  23  may be differentiated from a break in the second section including springs  24 ,  25 ,  26  since different changes in current are thereby generated in the ammeter of evaluation device  50 . 
     Different detection signals S 1 , S 2  may thus be generated in the first spring region and the second spring region, depending on the damage. 
     This may be used by the user or the manufacturer for diagnostic purposes, for example, and for a statistical analysis of occurring faults. 
     Although the present invention has been explained on the basis of micromirror arrays, it is not limited to them but instead may also be applied to other micromechanical components including spring elements, for example, sensors or actuators. 
     The geometries depicted here are intended only as examples and may be varied arbitrarily.