Abstract:
An optic device with a variable operating mode comprises a micromirror which can be obscured by means of an electrostatically controlled microshutter. In the operating condition of the microshutter, the petal of this adheres over a substrate to allow a beam of light to reach the mirror. In the condition at rest, the petal is curled up and one of its surfaces receives the beam of light and reflects it in all directions, at the same time preventing this from reaching the mirror.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to electrostatically controlled optic devices with a variable operating mode, of the type comprising:
         a fixed support including a substrate in the form of a lamina a few millimeters or centimeters thick,   an electrode composed of a film of electrically conductive material a few tens or hundreds of nanometers thick, applied to one side of the lamina constituting the substrate,   a dielectric or ferroelectric insulating film with a thickness ranging from 0.1 micrometers to a few tens of micrometers, applied over the film constituting said electrode, and   a movable petal, comprising a film of electrically conductive material, with a thickness ranging from a few fractions of micron to a few microns, having only an end portion connected rigidly to said insulating film and designed to assume an operating condition, in which it adheres completely with one of its surfaces, through electrostaticity, over said insulating film when an electric voltage is applied between said electrode and said petal, and a condition at rest, curled up, towards which the petal is drawn by its own elasticity when no electric voltage is applied, and in which a predominant portion of the aforesaid surface of the petal is spaced from said insulating film.       

   2. Background Art 
   A device of this type was proposed for example in the European patent application EP-A-1 008 885 by the same Applicant. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to produce an improved device of the type indicated above which is susceptible to various applications, among which in particular application for the production of an infrared spectrophotometer, the operation of which is reliable and efficient. 
   With a view to attaining this object, the invention relates to a device of the type indicated above, wherein said surface of the petal capable of adhering to the insulating layer is predisposed as a reflecting surface, designed to reflect and diffuse in all directions a beam of light incident on it when the petal is in the position at rest, and wherein over said substrate a mirror is predisposed designed to receive and reflect said beam of light when this is not intercepted by the electrostatically controlled petal, and when the latter is in its operating position, so that said device constitutes a micromirror that can be obscured by means of an electrostatically controlled microshutter. 
   The device thus produced has the advantage that the characteristics and the quality of the mirror do not depend on the micromachinings utilized to produce the petal. 
   The aforesaid mirror has a substrate which may be composed of the same surface of the substrate to which the petal adheres, or by an additional substrate applied over the substrate of the petal. The mirror may be disposed with the reflecting surface parallel to the surface of the substrate of the petal, or inclined in relation to this. 
   It is possible to provide a matrix arrangement of a plurality of micromirrors associated with electrostatically controlled microshutters according to the arrangement described above. A matrix of this type may, for example, be utilized advantageously in an infrared spectrophotometer, in which the micromirrors of the matrix are selected, by means of the relative microshutters, in order to select predetermined frequencies of a beam of light with dispersed chromatic components. 
   A further advantage of the device according to the invention resides in the fact that the petal supplied with electric voltage is never struck by the beam of light and therefore does not become nearly as hot as it would if the surface of the petal were to serve as a micromirror, thus allowing more intense beams to be modulated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention shall become apparent from the description below with reference to the accompanying drawings, provided purely as a non-limiting example, in which: 
       FIGS. 1 ,  2  are schematic sectional views which show a first embodiment of a micromirror with electrostatically controlled microshutter, in the condition at rest and in the operating condition of the petal, 
       FIG. 3  shows a variant of  FIG. 2 , and 
       FIG. 4  shows a variant in the direction of the mirror of the device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 ,  2  show a first embodiment of the device according to the invention. The device, indicated as a whole with the reference numeral  1 , comprises a fixed support  2  including a substrate  3  generally composed of a lamina of glass or plastic material a few millimeters or centimeters thick. In general, the thickness of the substrate  3  may range from a few micrometers to a few nanometers. In the device according to the invention the substrate  3  may be transparent or non-transparent. A layer  4  of conducting material, a few tens or hundreds of nanometers thick, which defines an electrode of the device, is produced on the surface of the substrate  3  by evaporation, spin-coating, screen-printing or dipping. More specifically, the thickness of the electrode  4  may range from 10 to 200 nanometers. The conductive layer  4  is subsequently insulated with a layer  5  of dielectric or ferroelectric insulating material, the thickness of which may vary from 0.1 micrometers to a few tens of micrometers, typically from 0.8 to 3 micrometers. This layer  5  can be obtained by screen-printing, spin-coating or dipping. The reference numeral  6  indicates the movable part of the device which is composed of a metallic film with a thickness ranging from a few fractions of micron to a few microns (petal). The petal  6  has an end portion  6   a  connected rigidly to the exposed surface of the insulating layer  5 , while the remaining part tends to assume, through its elasticity, a curled up configuration when at rest, shown in FIG.  1 . The curled up configuration may naturally also differ from the one shown in this figure, as it generally suffices for the petal in its position at rest to be raised and spaced from the surface of the insulation layer  5 . The dimensions (length and width) of the petal  6  vary as a function of the type of shutter required and the type of matrix in which this is destined to be inserted. In  FIGS. 1 ,  2  the block indicated with 7 schematically shows the means to apply an electric voltage between the electrode  4  and the petal  6 . By applying this voltage, the petal  6  is uncurled through electrostaticity on the surface of the insulating layer  5  adhering over this. If, on the other hand, there is no voltage between the petal  6  and the electrode  4 , the petal  6  assumes the configuration at rest shown in FIG.  1 . 
   According to the invention, the surface  6   b  of the petal  6  which adheres to the insulating layer  5  in the operating condition shown in  FIG. 2 , is predisposed to constitute a reflecting surface which, in the condition at rest of the petal ( FIG. 1 ) is designed to reflect and diffuse in all directions a beam of light L incident on it. Again according to the invention, over the fixed support  2 , and in particular over the portion  6   a  of the petal  6  which adheres to the fixed support, a mirror M is provided which is able to receive the beam of light L only when the petal  6  is in its operating condition shown in FIG.  2 . In this condition, the beam of light L is received by the mirror M and reflected in a direction LR. The petal  6  therefore constitutes an electrostatically controlled microshutter which is able to enable or disable the arrival of the beam of light L over the mirror M. This mirror is not composed of the same upper surface of the petal  6 , but comprises a reflecting layer S, for example composed of a film of gold, applied over a substrate. In the case in  FIGS. 1 ,  2 , the substrate of the mirror is the same substrate as the petal  6 .  FIG. 3  shows a solution in which the mirror M comprises a layer of gold S deposited over the layer of silicon  71  in turn fixed over the portion  6   a  of the petal  6  and over the insulating layer  5  by means of a layer  8  of heat insulating binding material. 
   As already shown above, it is possible to provide a linear array or a bi-dimensional matrix composed of a plurality of devices of the type shown in  FIGS. 1 ,  2  or in FIG.  3 . In this case electronic control means are naturally provided designed to control the application of voltage to the various electrostatically controlled microshutters to select predetermined frequencies of a beam of light with suitably dispersed chromatic components. A device of this type may be applied advantageously in an infrared spectrophotometer. As the mirror M is produced as a separate element from the petal  6 , the quality of the mirror does not depend on the micromachinings utilized to produce the petals and may therefore, if necessary, be extremely high. The petal  6 , supplied with electric voltage, is never struck directly by the beam of light and therefore does not become nearly as hot, allowing modulation of more intense beams. 
     FIG. 4  shows a variant in which the mirror M is directed with its reflecting surface inclined in relation to the plane of the substrate  3 , unlike the situation in  FIGS. 1 ,  2  and  3 , in which the mirror M is parallel to the surface of the substrate  3 . 
   Naturally, without prejudice to the principle of the finding, the constructional details and embodiments may vary widely in relation to what is described and shown purely as an example, without however departing from the scope of the present invention. 
   For example, a refractive or diffractive optic element may be associated with the mirror M. The reflecting surface of the petal may be provided with thin optic elements, such as binary diffractive optic elements. The mirror may also be composed of diffractive optic microridges of a height ranging from 0.2 to 2 microns.