Abstract:
A thermal ink jet printhead ( 40 ) for the emission of droplets of ink on a print medium ( 46 ) comprises a reservoir ( 103 ) containing ink ( 142 ), a die ( 61 ), a slot ( 102 ) engraved in said die ( 61 ) and a plurality of ejectors ( 73 ), each of which in turn comprises a chamber ( 74 ), a resistor ( 27 ) and a nozzle ( 56 ), each of said chambers ( 74 ) being put in fluid communication with said slot ( 102 ) through a plurality of elementary ducts ( 72 ) lying on a different plane from the bottom ( 67 ) of said chamber ( 74 ).

Description:
This application is a divisional application of and claims priority from application Ser. No. 10/169,114, filed on Jun. 27, 2002 now U.S. Pat. No. 6,719,913, of the same title; and applicant herewith claims the benefit of priority of PCT/IT00/00534 filed on Dec. 19, 2000, which was published Under PCT Article 21(2) in English, and of Application No. AO99A00002 filed in Italy on Dec. 27, 1999. 
    
    
     TECHNICAL FIELD 
     This invention relates to a printhead used in equipment for forming, through successive scanning operations, black and colour images on a print medium, usually though not exclusively a sheet of paper, by means of the thermal type ink jet technology, and in particular to the head actuating assembly and the associated manufacturing process. 
     BACKGROUND ART 
     Depicted in  FIG. 1  is an ink jet colour printer on which the main parts are labelled as follows: a fixed structure  41 , a scanning carriage  42 , an encoder  44  and, by way of example, printheads  40  which may be either monochromatic or colour, and variable in number. 
     The printer may be a stand-alone product, or be part of a photocopier, of a “plotter”, of a facsimile machine, of a machine for the reproduction of photographs and the like. The printing is effected on a physical medium  46 , normally consisting of a sheet of paper, or a sheet of plastic, fabric or similar. 
     Also shown in  FIG. 1  are the axes of reference: 
     x axis: horizontal, i.e. parallel to the scanning direction of the carriage  42 ; y axis: vertical, i.e. parallel to the direction of motion of the medium  46  during the line feed function; z axis: perpendicular to the x and y axes: i.e. substantially parallel to the direction of emission of the droplets of ink. 
     The composition and general mode of operation of a printhead according to the thermal type technology, and of the “top-shooter” type in particular, i.e. those that emit the ink droplets in a direction perpendicular to the actuating assembly, are already widely known in the sector art, and will not therefore be discussed in detail herein, this description instead dwelling more fully on some only of the features of the heads and the manufacturing process, of relevance for the purposes of understanding this invention. 
     The current technological trend in ink jet printheads is to produce a large number of nozzles per head (≧300), a definition of more than 600 dpi (dpi=“dots per inch”), a high working frequency (≧10 kHz) and smaller droplets (≦10 pl) than those produced in earlier technologies. 
     Requirements such as these are especially important in colour printhead manufacture and make it necessary to produce actuators and hydraulic circuits of increasingly smaller dimensions, greater levels of precision, narrow assembly tolerances. It is important in particular to ensure that the volume and speed of the droplets subsequently emitted are as constant as possible, and that no “satellite” droplets are formed as these, with a trajectory generally different from the main droplets, are distributed randomly near the edges of the graphic symbols, reducing their sharpness. 
       FIG. 2  shows an enlarged axonometric view of an actuating assembly  111  of an ink jet printhead according to the known art, made of a die  100  of semiconductor material (usually Silicon), on the upper face of which resistors  27  have been made for emission of the droplets of ink, driving circuits  62  for driving the resistors  27 , soldering pads  77  for connecting the head to an electronic controller not shown in the figure, and which bears a pass-through slot  102  through which the ink flows from a reservoir not shown in the figure. Around the upper edge of the slot  102  a basin  76  has been made, the characteristics and functions of which are as described in detail in Italian patent application TO 98A 000562. Affixed to the upper face of the die is a layer  105  of photopolymer having, usually though not exclusively, a thickness less than or equal to 25 μm in which, by means of known photolithographic techniques, a plurality of ducts  53  and a plurality of chambers  57  positioned locally to the resistors  27  having been made. Stuck on the photopolymer  105  is a nozzle plate  106 , generally made of a plate of gold-plated nickel or kapton, of thickness less than or equal to 50 μm, bearing a plurality of nozzles  56 , each nozzle  56  being in correspondence with a chamber  57 . In the current technology, the nozzles  56  have a diameter D of between 10 and 60 μm, while their centres are usually spaced apart by a pitch A of 1/300 th  or 1/600 th  of an inch (84.6 μm or 42.3 μm). Generally, though not always, the nozzles  56  are arranged in two rows parallel to the y axis, staggered one from the other by a distance B=A/2, in order to double the resolution of the image in the direction parallel to the y axis; the resolution thus becomes 1/600 th  or 1/1200 th  of an inch (42.3 μm or 21.2 μm). The x, y and z axes, already defined in  FIG. 1 , are also shown in  FIG. 2 . 
       FIG. 3  is an axonometric enlargement of two chambers  57 , adjacent and communicating with the slot  102  through the basin  76  and the ducts  53  made in the layer of photopolymer  105 . Normally the ducts  53  have a length l and a rectangular cross-section having a depth a and a width b. The chambers  57  have a depth d, substantially equal to the depth a of the ducts  53 . 
     A section of an ejector  55  can be seen in  FIG. 4 , where the following are shown, in addition to the items already mentioned: a reservoir  103  containing ink  142 , a droplet  51  of ink, a vapour bubble  65 , a meniscus  54  in correspondence with the surface of separation between the ink and the air, an external edge  66  and arrows  52  which indicate the prevalent direction of motion of the ink. 
     To describe the operation of an ejector for a thermal type ink jet printhead, an electrical analogy is used, for which the following equivalences are established: 
     V=electrical voltage in volt equivalent to: pressure in N/M 2 ; 
     I=current in A equivalent to: flow rate in m 3 /s; 
     R=resistance in ohm equivalent to: hydraulic resistance in
 
N/m 2 /m 3 /s=N s/m 5 ;
 
L=Inductance in henry equivalent to the ratio between the mass of the column of liquid that fills the duct and the square of the section of the duct; this ratio is called “hydraulic inertance”, and is measured in kg/m 4 ;
 
C=capacitance in farad equivalent to: hydraulic compliance
 
in m 3 /N/m 2 =m 5 /N.
 
     In the equivalent diagram of  FIG. 5  the bubble is represented as a variable capacitance C b . There is a front leg  70 , equivalent to the whole formed by the chamber  57 , the nozzle  56 , the meniscus  54  and the droplet  51 , and a rear leg  71 , which represents the section of the hydraulic circuit between the chamber  57  and the reservoir  103 . 
     The front leg  70  comprises a fixed impedance L f , R f  corresponding substantially to the chamber  57 , a variable impedance L u , R u  corresponding substantially to the nozzle  56 , and a deviator T which, during the step in which the droplet  51  is formed, inserts a variable resistance R g  substantially corresponding to the droplet, whereas, during the steps of withdrawal of the meniscus  54 , of filling of the nozzle, of subsequent oscillation and damping of the meniscus, inserts a capacitance C m  substantially corresponding to the meniscus itself. 
     Ejection of the ink takes places in accordance with the following steps:
     a) The electronic control circuit  62  supplies energy to the resistor  27 , so as to produce local boiling of the ink with formation of the bubble  65  of steam in expansion. During this step, in the equivalent electric circuit of  FIG. 5  the variable resistance R g  is inserted. The bubble  65  generates two opposing flows: I p  (to the reservoir  103 ) and I a  (to the nozzle  56 ).   b) The electronic circuit  62  terminates the delivery of energy to the resistor  27 , the vapour condenses, the bubble  65  collapses, the droplet  51  detaches itself, the meniscus  54  withdraws emptying the nozzle  56 . The two opposing flows I p  and I a  remain. In this step, in the equivalent circuit of  FIG. 5  the capacitance C m  corresponding to the meniscus  54  is inserted.   c) The bubble  65  has disappeared, the meniscus  54  demonstrates its capillarity and goes back towards the outer edge  66  of the nozzle  56  sucking new ink  142  into the nozzle  56 . Its return completed, the meniscus  54  remains attached to the outer edge  66  by oscillating and behaving like a vibrating membrane. In the equivalent electric circuit of  FIG. 5  the capacitance C m  is still inserted. During this step the equivalent circuit of the ejector  55  is simplified as sketched in  FIG. 6 , where C m  represents the capacitance of the meniscus, while R and L represent respectively the sum of all the resistances and of all the inductances present between the meniscus  54  and the reservoir  103 . In addition, the flows I p  and I a  converge into a single flow i.   

     To obtain an optimal operation of the ejector  55 , it is necessary for the meniscus  54 , at the end of the step c), to reach the idle state rapidly and without oscillating. In this way the ink  142  does not wet the outer surface of the nozzle plate  106 , thereby avoiding alterations of speed and volume of the following droplets. 
     For a given nozzle  56  the parameters L u , R u  and C m , belonging to the front hydraulic part  70  of the ejector  55 , are set and therefore, to obtain the values of R and L according to the criteria set down below, it is possible to act only on the design of the rear hydraulic part  71 . 
     The expression in function of the time i, which represents the flow, is given by the known relation: 
     
       
         
           
             
               
                 
                   i 
                   = 
                   
                     
                       
                         V 
                         m 
                       
                       L 
                     
                     * 
                     t 
                     * 
                     
                       ⅇ 
                       
                         
                           - 
                           t 
                         
                         
                           2 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           τ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where V m  represents the pressure generated by the meniscus  54 , which is negative during the filling step, and τ is the time constant, measured in seconds, of the RLC circuit of  FIG. 6 , equal to the ratio L/R. 
     For maximum speed in filling of the nozzle  56 , the flow i must be rendered maximal, and for this to happen L and τ must be rendered minimal. 
     Also, for the meniscus  54  to reach the idle state rapidly without oscillating, the equivalent circuit of  FIG. 6  must be “critical damping” type, and must for this purpose satisfy the known relation: 
     
       
         
           
             
               
                 
                   R 
                   = 
                   
                     2 
                     * 
                     
                       
                         L 
                         
                           C 
                           m 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     For a duct  53  of length l, the section of which has sides a and b with a&gt;&gt;b, the following known relations apply: 
     
       
         
           
             
               
                 
                   R 
                   ≅ 
                   
                     
                       12 
                       * 
                       ρ 
                       * 
                       υ 
                       * 
                       l 
                     
                     
                       
                         b 
                         3 
                       
                       * 
                       a 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   L 
                   ≅ 
                   
                     
                       ρ 
                       * 
                       l 
                     
                     
                       b 
                       * 
                       a 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   τ 
                   = 
                   
                     
                       L 
                       R 
                     
                     = 
                     
                       
                         b 
                         2 
                       
                       
                         12 
                         * 
                         υ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     where ρ is the density of the ink in kg/m 3 , ν is the viscosity of the ink in m 2 /s, and all lengths are measured in metres. 
     The time constant τ is a function of the width b, while it is independent of both the depth a and the length l. 
     It is possible to determine a value of b which gives values R and L such as to produce the critical damping, according to the expression (2). However the same value of b, substituted in (5), provides a value of τ which limits the flow i, according to the relation (1), and accordingly limits the emission frequency of the droplets. Moreover, it is not possible to modify either depth a or length l at will, as these parameters are subject to other technological and functional constraints, not described as they are not essential for the understanding of this invention. 
     To increase the emission frequency of the droplets, it is necessary to make the time constant τ much shorter than that obtained in the known art, while at the same time satisfying the critical damping condition: this problem is solved in this invention by making a plurality of N ducts in parallel, as will be seen in detail in the description of the preferred embodiment. 
     Some further drawbacks with the chambers  57  according to the known art are now mentioned, which have three continuous lateral walls and a fourth wall interrupted by the duct  53  of non-negligible width. In this situation the bubble  65  collapses prevalently in the direction of the resistor  27  underneath, which is thus subjected to greater wear on account of the known phenomenon of cavitation. In addition, the collapse of the bubble is dissymmetrical as it is attracted to the wall opposite the duct  53 : this cause a dissymmetry in the motion of the meniscus  54 , with a resulting deviation of the terminal part of the droplet  51  and the formation of satellite droplets having a different direction from the droplet  51 . 
     In this invention the duct  53  is substituted by N ducts placed in parallel and communicating with the chamber through the lower or upper wall, and consequently the four lateral walls of the chamber are continuous and symmetrical. 
     In U.S. Pat. No. 5,666,143 a solution is described in which the ink is brought to the chamber along multiple ducts, but these do not suffice to solve the problems reported. 
     DISCLOSURE OF THE INVENTION 
     It is an aspect of this invention is to render the emission frequency of the droplets of ink maximal by making the time constant τ of the ejector as short as possible, while at the same time satisfying the condition of critical damping of the meniscus. 
     It is an aspect of an embodiment of the invention to increase the degrees of freedom of the design of the ejector, by having the additional parameter consisting of the number N of elementary ducts in parallel. 
     It is an aspect of an embodiment of the invention to increase the life span of the resistor by making a chamber with four continuous walls, which promotes symmetrical collapse of the bubble in the direction of these walls and not towards resistor: this lowers the harmful effects of cavitation during collapse of the bubble. 
     It is an aspect of an embodiment of the invention to avoid the formation of satellite droplets by achieving a symmetrical movement of the meniscus made possible by the chamber with four continuous walls. 
     It is an aspect of an embodiment of the invention to filter the ink of any impurities that may be present. 
     These and other objects, characteristics and advantages of the invention will be apparent from the description that follows of a preferred embodiment, provided purely by way of an illustrative, non-restrictive example, with reference to the accompanying drawings. 
    
    
     
       LIST OF FIGURES 
       FIG.  1 —is an axonometric view of an ink jet printer; 
       FIG.  2 —is an enlarged view of an actuating assembly made according to the known art; 
       FIG.  3 —represents two emission chambers, according to the known art; 
       FIG.  4 —represents a sectioned view of one ejector of the head, according to the known art; 
       FIG.  5 —represents an equivalent electrical diagram of the hydraulic circuit of an ejector of the head; 
       FIG.  6 —represents a simplified equivalent wiring diagram of the hydraulic circuit of an ejector of the head; 
       FIG.  7 —represents an axonometric view of a portion of the actuating assembly of the head, made according to this invention; 
       FIG.  8 —represents an axonometric view of the emission chamber, according to a different visual angle from that of  FIG. 7 ; 
       FIG.  9 —represents a section according to the plane AA, shown in  FIG. 7 ; 
       FIG.  10 —illustrates the flow of the process for manufacture of the actuating assembly of  FIG. 7 ; 
       FIG.  11 —represents a section view of the actuating assembly, at the start of the manufacturing process; 
       FIGS. from  12  to  14 —represent the actuating assembly as it is during later steps of the manufacturing process; 
       FIG.  15 —illustrates the flow of the manufacturing process of an actuating assembly according to a second embodiment; 
       FIG.  16 —represents an enlarged view of an actuating assembly, according to a third embodiment; 
       FIG.  17 —represents a section view and a view of the lower face of the actuating assembly, according to the third embodiment; 
       FIG.  18 —represents section view and a view of the lower face of the actuating assembly, according to a fourth embodiment; 
       FIG.  19 —represents an enlarged view of the actuating assembly, according to a fifth embodiment; 
       FIG.  20 —represents a section view of the actuating assembly, according to the fifth embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 7  illustrates a portion of the actuator for printhead, monochromatic or colour, comprising an ejector  73  according to the invention. For simplicity&#39;s sake, the other parts of the head, being already known and not concerning the invention, are not depicted. The following are shown in the figure:
         a portion of a die  61 ;   a substrate  140  of Silicon P belonging to the die  61 ;   a slot  102  cut into the substrate  140 ;   the basin  76 , having depth c;   a layer  107  of photopolymer, according to the invention;   a chamber  74  according to the invention, made in the layer  107  of photopolymer, having depth d;   a bottom  67  of the chamber  74 ;   lateral walls  68  of the chamber  74 ;   the resistor  27  on the bottom  67  of the chamber  74 ;   elementary ducts  72  according to the invention, which convey the ink  142  from the basin  76  to the chamber  74 , each having depth f, width g and length l.       
       FIG. 8  illustrates the chamber  74  from a different visual angle, indicated by the reference axes, which shows the outlet of the elementary ducts  72  in the chamber  74 . The ducts  72  are located under the layer  107  of photopolymer, and are therefore at a lower level than the bottom  67  of the chamber  74 : in this way, a tank  63  is made which hydraulically connects the ducts  72  with the chamber  74 . 
       FIG. 9  shows the ejector  73  sectioned according to a plane AA, indicated in  FIGS. 7 and 8 . 
     According to a construction variant of the preferred embodiment, the basin  76  is missing, and the ducts  72  face directly on to the slot  102 . 
     A method is now described for calculating the correct number N of elementary ducts  72 . 
     The time constant τ is a function of the width g of each single duct  72 , whereas it is independent of the number N of ducts in parallel, as indicated by the following relation, analogous to (5): 
     
       
         
           
             
               
                 
                   τ 
                   = 
                   
                     
                       L 
                       R 
                     
                     = 
                     
                       
                         g 
                         2 
                       
                       
                         12 
                         * 
                         υ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     It is therefore possible to obtain as short a time constant τ as possible by selecting the smallest value of g possible, compatibly with technological feasibility. 
     Conversely, if we assign τ a predetermined value, we obtain:
 
 g =√{square root over (12*ν*τ)}  (7)
 
     In practice, the width g according to this invention is, though not exclusively, between 3 and 15 μm. 
     Having thus determined the geometrical dimensions of a single duct  72 , we obtain values R′ and L′ of resistance and inductance equivalent to each duct  72  by means of the following relations, similar to (3) and (4): 
     
       
         
           
             
               
                 
                   
                     R 
                     ′ 
                   
                   ≅ 
                   
                     
                       12 
                       * 
                       ρ 
                       * 
                       υ 
                       * 
                       l 
                     
                     
                       
                         g 
                         3 
                       
                       * 
                       f 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
             
               
                 
                   
                     L 
                     ′ 
                   
                   ≅ 
                   
                     
                       ρ 
                       * 
                       l 
                     
                     
                       g 
                       * 
                       f 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     The total resistance R and total inductance L of the equivalent circuit with the plurality of ducts  72  in parallel are calculated using the known formula for impedances in parallel, and are:
 
 R=R′/N   (10)
 
 L=L′/N   (11)
 
     It is now possible to obtain the value of N by substituting the expressions (10) and (11) in (2), which becomes: 
     
       
         
           
             
               
                 
                   
                     
                       R 
                       ′ 
                     
                     N 
                   
                   = 
                   
                     2 
                     * 
                     
                       
                         
                           L 
                           ′ 
                         
                         
                           N 
                           * 
                           
                             C 
                             m 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     and which allows us to obtain 
     
       
         
           
             
               
                 
                   N 
                   = 
                   
                     
                       
                         ( 
                         
                           R 
                           ′ 
                         
                         ) 
                       
                       2 
                     
                     * 
                     
                       
                         C 
                         m 
                       
                       
                         4 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           L 
                           ′ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     The value thus obtained for N is generally not an integer, and must be rounded to the nearest whole number: this causes a slight deviation from the condition of critical damping, which may be recovered with a slight variation of the length l of the elementary duct  72 . 
     The manufacturing process of an ejector  73  for a monochromatic or colour ink jet printhead  40  according to the invention is effected according to the steps indicated in the flow diagram of  FIG. 10 .  FIGS. 11 to 14  represent the ejector  73  in successive stages of the work. 
     In the step  201 , by means of a known process, a wafer is made available containing a plurality of dice completed solely in the control circuits  62  and in the resistors  27 . Visible in  FIG. 11  is a section of a portion of a die  61  in which an ejector will be made. The following are indicated:
         a portion of the die  61 ;   the substrate  140  of Silicon P belonging to the die  61 ;   a LOCOS insulating layer  35  of SiO 2 ;   a BPSG “interlayer”  33 ;   the resister  27 ;   a layer  30  of Si 3 N 4  and SiC for protection of the resistors;   a conducting layer  26 , made of a layer of Tantalum covered by a layer of Gold.       

     In the step  202 , a photoresist is laid over the entire surface of the wafer. 
     In the step  203 , development is effected of the photoresist, by means of a first mask not depicted in any of the figures, of the geometry of the elementary ducts  72 , of the basin  76  and of the tank  63 . 
     In the step  204 , dry etching (Tegol) is performed of the LOCOS+BPSG+Si 3 N 4  until the substrate  140  of Silicon is uncovered in the areas defined by the first mask in the previous step  203 . 
     In the step  205 , the elementary ducts  72 , the basin  76  and the tank  63  are etched into the Silicon using “dry” technology in the STS plant, with arrangements known to those acquainted with the sector art. Geometry of the etching is defined by the photoresist already developed in the step  203  according to the design of the first mask, reinforced by the layer of LOCOS+BPSG+Si 3 N 4  beneath. Referring back to  FIG. 7 , depth f of the channels is less than depth c of the basin  76  due to the different etching speed resultant on the different width of the etching front. If, as a non-restricting example, we assume f=10 μm, g=5 μm and a basin width of 300 μm, we obtain a depth c of the basin equal to approximately 20 μm. In general, the depth f is prevalently but not exclusively between 10 and 100 μm. At this stage of the work, the ejector is as shown in  FIG. 12 . 
     In the step  212 , the photoresist is removed and the wafer cleaned. 
     In the step  213 , the layer  107 , consisting of negative photopolymer, is laminated on the entire surface of the wafer. 
     In the step  214 , the layer  107  is developed according to the geometry of a second mask, non depicted in any of the figures, with the purpose of obtaining the chamber  74 , the plan of which includes the resistor  27  and the tank  63 , and uncovering the basin  76 , as illustrated in  FIG. 13 , where the dashed area represents the remaining photopolymer. 
     In the step  215 , the areas of the resistors  27  and of the soldering pads  77  are protected using a material that may be removed with water. 
     In the step  216 , the pass-through slot  102  is made by way of, for example, a sand blasting process. At this stage of the work, the zone of the ejector is as shown in  FIG. 14 . 
     In the step  217 , the usual completion and finishing operations are carried out, known to those acquainted with the sector art. 
     Second Embodiment 
     The principle of the invention is also applicable in cases where the basin  76  is made with a ratio between the depth c and the depth f of the elementary ducts  72  and of the tank  63  that is greater than what it would be naturally on account of the different etching speeds. As a non-restricting example, for the basin  76  a depth c of between 20 and 100 μm may be selected, and for the ducts  72  and the tank  63  a depth f of between 5 and 20 μm. The production process is modified according to the flow diagram of  FIG. 15 , in which the following steps are inserted after the step  204 . 
     In the step  205 ′, elementary ducts  72  and the tank  63  are etched into the Silicon with “dry” technology on the STS plant. The depth f of the etching is prevalently but not exclusively limited to between 5 and 20 μm. In this stage, the basin  76  may or may not be etched, depending on the design of the first mask. 
     In the step  206 , the photoresist previously laid in the step  202  and developed in the  203  is removed. 
     In the step  207 , lamination is performed of a “dry film” type photoresist over the entire surface of the wafer, which in this way covers and protects the area occupied by the\ ducts  72  and the tank  63 . 
     In the step  210 , development is effected of the second photoresist, by means of a third mask not depicted in any of the figures, so as to leave uncovered only the area of the basin  76 . 
     In the step  211 , a further etching is made in the Silicon, this time of the basin  76 , using “dry” technology in the STS plant. The depth of this etching is in this way greater than that which would be obtained by the step  205 ′ alone, and prevalently but not exclusively between 20 and 100 μm. 
     Once this step is completed, the process continues to step  212 , as already described for the preferred embodiment. 
     Third Embodiment 
     A variant in the known art consists in producing the nozzles directly on a “flat cable”, which in this way also performs the function of nozzle plate, and is represented in  FIG. 16  by means of an enlarged view of an actuating assembly  112 . According to this embodiment, the nozzle plate  106  is replaced by a flat cable with nozzles  130 , which comprises the nozzles  56 ′. The following may be seen in the figure: 
     the die  100 , made according to the known art already illustrated in  FIG. 2 ;
         the layer of photopolymer  107 , made according to the preferred embodiment, which comprises the chambers  74  having the continuous lateral walls  68 ;   the flat cable with nozzles  130 , made for instance of Kapton;   an upper face  113  of the flat cable with nozzles  130 ;   a lower face  114  of the flat cable with nozzles  130 .       

       FIG. 17  presents a section of the flat cable with nozzles  130  and a view of its lower face  114 , limited to a single ejector. The elementary ducts  72 ′ are made directly on the lower face  114  of the flat cable with nozzles  130 , using for instance an excimer laser. 
     Fourth Embodiment 
     This embodiment is represented in  FIG. 18  by way of a section of the flat cable with nozzles  130  and a view of the lower face  114 , limited to a single ejector. The elementary ducts  72 ′ are again made directly on the lower face  114  of the flat cable with nozzles  130 , together with a chamber  74 ′, using for instance an excimer laser, but the layer  107  is missing. 
     Fifth Embodiment 
     The principle of the invention is also applicable in cases where the feeding of the ink takes place on the two sides of the die, according to a variant of the known art disclosed in the U.S. Pat. No. 5,278,584.  FIG. 19  represents a die  183  with lateral feeding of the ink and a flat cable with nozzles  180  associated therewith, having an upper face  115  and a lower face  116 , produced according to said patent. 
       FIG. 20  represents a section view of a die with lateral feeding  183 ″, of a photopolymer  107 ″ in which a plurality of chambers  74 ″ has been made, of a flat cable with nozzles  180 ″ which present an upper face  115  and a lower face  116 . A plurality of nozzles  56 ″ and elementary ducts  72 ″ are made in the lower face  116  of the flat cable with nozzles  180 ″, similarly to what was described in the third embodiment. The ink reaches the chamber  74 ″ from the sides of the dice  183 ″ through the elementary ducts  72 ″. 
     A variant of the fifth embodiment may be obtained by also etching the chambers directly in the lower face  116  of the flat cable with nozzles  180 ″ and eliminating the layer of photopolymer  107 ″, similarly to what was described for the fourth embodiment. 
     A further variant of the fifth embodiment may be obtained by etching the elementary ducts in the silicon of the dice  183 , on a plane below the layer  107 ″, similarly to what was described for the preferred embodiment. The elementary ducts face on to a depression produced by a “scribing” operation, known to those acquainted with the sector art: in this way, the cut with the diamond wheel, which separates the dice  183 , does not touch the ends of the elementary ducts directly, and thus avoids damaging them.