Abstract:
A semiconductor antifuse device that utilizes a resistive heating element as both a heating source or fuse blowing and as part of the fuse link. The antifuse device may also be utilized as a fuse and the antifuse or fuse embodiment can be programmed and read with the same two electrodes. The antifuse or fuse is well suited for use and efficient fabrication in a printhead apparatus or other circuit arrangements.

Description:
FIELD OF THE INVENTION 
     The present invention relates to semiconductor fuses and antifuses and, more specifically, to an improved antifuse. 
     BACKGROUND OF THE INVENTION 
     Various semiconductor fuses and antifuses are known in the art. These devices, particularly fuses, are typically used to store data. Conventional fuses operate such that they have a low resistance when initially fabricated and a dramatically increased resistance by application of a sufficient pulse of energy to cause the fuse to fail. This type of technology is often used, for example, in programmable read-only memory (PROM) devices. The programming is achieved by applying a sufficient current to desired ones of the fuses to cause those fuses to fail, thus permanently storing data, e.g., blown fuse=1, closed fuse=0. 
     In contrast to fuses (which have low resistance in an initial state), antifuses typically have a larger resistance in an initial state and less resistance in a “blown” or activated state. Antifuses are also used for data storage. One prior art antifuse structure is that of ACTEL and this structure consists of a thin oxide/nitride/oxide (ONO) layer sandwiched between a heavily doped n+ diffused region and a heavily doped n+ polysilicon electrode. The presence of the ONO layer isolates the electrodes and thus the structure has a large resistance as fabricated. By applying a sufficiently large voltage pulse to this structure, the ONO dielectric will break down leading to a large current flow through the dielectric. This in turn causes localized heating and the resultant formation of a short between the electrodes. Once this short has formed, the resistance of the structure typically drops from greater than 10,000 Ohms to approximately 100 Ohms, depending on the current allowed to flow during the fuse programming. 
     Another prior art antifuse is disclosed in U.S. Pat. No. 5,572,050 issued to Cohen. This antifuse includes a heating element beneath a pair of electrodes separated by a thermally transformable dielectric material. Applying current to the heating element causes the transformable dielectric to melt and break down which permits formation of a permanent link that programs the antifuse. 
     Both of the above described antifuse structures rely on a dielectric material between the electrodes to provide an initial resistance value. Dielectric antifuse embodiments are disadvantageous, amongst other reasons, in that they require at least four electrodes, two to program and two to read. A need exists for an antifuse that requires fewer electrodes. 
     Another disadvantageous aspect of prior art antifuses is that when used with other circuitry (i.e., fabricated on the same die), the dielectric-based antifuse requires significant additional processing, including deposition (or growth) of appropriate dielectric material. A need thus exists for a semiconductor fuse/antifuse that can be manufactured in an efficient manner. 
     Yet another disadvantageous aspect of prior art antifuses is that they require a significantly large programming signal. A lower power signal for programming and reading are advantages in that they lead to reduced physical stress and more efficient energy use. 
     Needs also exist for a fuse or antifuse device that has enhanced structural integrity (i.e., it can withstand thermal stress, corrosive ink and other deleterious forces) and a fuse or antifuse that has tri-state properties. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a semiconductor fuse or antifuse that is programmable and readable with the same two electrodes. 
     It is another object of the present invention to provide a semiconductor fuse/antifuse with enhanced structural integrity. 
     It is another object of the present invention to provide such a semiconductor fuse/antifuse that can be used and efficiently fabricated in a printhead environment. 
     It is another object of the present invention to provide a tri-state fuse/antifuse device. 
     And it is yet another object of the present invention to provide a low power fuse/antifuse device. 
     These and related objects of the present invention are achieved by use of a semiconductor antifuse device as described herein. 
    
    
     The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of a semiconductor antifuse in accordance with the present invention. 
     FIG. 2 is a side view of the antifuse in a blown state in accordance with the present invention. 
     FIG. 3 is a side view of a partially blown (or tri-state) configuration of the antifuse in accordance with the present invention. 
     FIGS. 4-6 are various embodiments of fused geometries in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a diagram of a semiconductor antifuse  30  in accordance with the present invention is shown. A firing chamber  20  is also shown fabricated on the same substrate as antifuse  30 . Antifuse  30  can be fabricated alone, with a firing chamber or with another circuit or device without departing from the present invention. 
     Antifuse  30  preferably includes a semiconductive or like substrate  32 , a resistive fuse element  33 , electrodes  34 , a passivation or other insulation layer  35  and a conductive a protection layer  36 . The resistive fuse element  33  is preferably a resisitive heating type element similar to the resistive heating element used in ink jet print head and is generally referred to in the following description as “resistive element  33 .” As discussed in more detail below conductive layer  36  provides both protection for resistive element  33  (by increasing the structural integrity of insulation layer  35 , for example, for a fuse as discussed with reference to FIG. 3) and conduction for a blown or “active” antifuse. Since conductive layer  36  provides conduction (short circuit) for antifuse  30  (see FIG.  2 ), the function of the antifuse is unaffected by ink leakage because leaked ink also causes a short circuit. 
     Referring to FIG. 2, a side view of antifuse  30  in a blown state in accordance with the present invention is shown. When an appropriate current is propagated through resistive element  33  and electrode  34 , the resistive element will blow. Empirical evidence indicates that the remaining portions  33 A, 33 B of resistive element  33  will spall and melt generally as shown. The passivation layer  35  may be melted and deformed and the surrounding thin film layers may be cracked or have other stress damage. Upon exposure to sufficient current, the resistive element portions  33 A, 33 B and passivation layer  35  and conductive layer  36  deform sufficiently such that portions  33 A, 33 B contact the conductive layer forming a low resistance path between the electrodes. 
     The initial resistance across the electrodes in FIG. 1 may be less than approximately 1000 ohms and may further be in the range of approximately 50-200 Ohms, depending on the design parameters of the resistive element. The resistance across the electrodes in FIG. 2, however, may be in the order of 5-20 Ohms. For an embodiment with tantalum (Ta) as the conductive overlayer, a resistance reduction on the order of approximately 5 to 10× is typical. Larger reductions should be possible if a lower resistance metal overlayer, such as Au or Al or the like, is used. 
     Referring to FIG. 3, a side view of a partially blown (or tri-state) configuration of antifuse  30  in accordance with the present invention is shown. In the illustration of FIG. 3, a sufficient current is passed through resistive element  33  to blow the resistive element. The current amount, however, is less than that used in FIG.  2  and is sufficient to cause breakage of the resistive element, but not sufficient enough to cause a deformation of the resistive element, passivation layer and conductive layer such that a signal path through the conductive layer is formed. The device of FIG. 3 has a high resistance like a blown fuse. Accordingly, antifuse  30  can be transformed from an initial resistance level to a low resistance level or to a high resistance level, depending on the applied programming current. 
     Referring again to FIG. 1, antifuse  30  may be advantageously used and fabricated in a printhead arrangement (and in other circuit environments). Firing chamber  20  preferably includes resistive element  23 , electrodes  24 , passivation or insulation layer  25 , conductive protection layer  26 , barrier level  27 , ink well  28 , nozzle  29  and nozzle plate  21 . Firing chambers are known in the art. Antifuse  30  can be efficiently and advantageously used with firing chamber  20  and the like because several components of each device can be formed during the same process steps. For example, resistive elements  33 , 23 , electrodes  34 , 24 , passivation or insulation layers  35 , 25 , and conductive protection layers  36 , 26  may be formed in corresponding process steps. These paired components would thus be formed of substantially the same material. 
     FIG. 1 also illustrates control logic  40  that propagates firing signals over line  42  to firing chamber  20  and programming and/or read signals over line  41  to antifuse  30 . 
     With respect to programming pulses and component configuration, in a preferred embodiment, application of a 5V, one ms pulse is sufficient for link formation, i.e., antifuse activation, on resistive element widths from 2.5 to 5 um and lengths from 5 to 10 um. For resistive elements with 5 um length, this results in programming current from approximately 60-120 mA as width increases from 2.5 to 5 um. Programming currents for resistive elements with 10 um length will be approximately half this. Programming of the low resistance state will be more reliable when voltages and currents larger than those discussed immediately above are used for link formation. Programming of the high resistance state will require voltages (or current) that are approximately 50% lower than those discussed above and the use of longer programming pulses. It should be recognized that the actual programming current (time and magnitude, etc.) will vary with process, component size and characteristic resistivity of material used, etc., as would be apparent to one skilled in the art. 
     For rectangular resistive elements with L/W&gt;1, the programming current will be proportional to the resistive element width W. Reduction in programming current can be obtained by using pinch point designs or other geometric features designed to reduce programming current, for example, those discussed below with reference to FIGS. 4-6. As with all thermal structures, the exact programming currents needed for a given design will depend upon (1) the thickness of the passivation and conductive layers (e.g., as the thermal mass of the structure increases, heat dissipation increases and thus more energy is required to heat the structure to a given temperature) and (2) the geometry of the resistive element itself. 
     With respect to the thicknesses of the layers of antifuse  30 , the thicknesses may vary based on intended design and on improvements in processing techniques. Nonetheless, general thickness consideration include the following: Ta conductive layer 3000-6000 Å (will probably depend on desired value of low resistant link and materials used); passivation layer 3750-7500 Å (1000Å to 1 um with a nominal value of 4000 Å); electrode thickness (Al) 5000 Å (may depend on desired interconnect resistance); and resistive element thickness approximately 1000 Å (will vary with resistive element material and desired resistance). The resistive element  33  (and the resistive element  23  of FIG. 1) may be formed of any suitable resistive layer material. Suitable resistive layer material typically includes one or more metals and examples include, but are not limited to, aluminum, tantalum containing material (e.g., TaN, TaAl, TaAlO x ) and HfB 2 , etc., as is known in the art. 
     Referring to FIGS. 4-6, various embodiments of fuse/antifuse geometries in accordance with the present invention are shown. These fuses  60 ,  70 ,  80 , have geometries that channel programming current to “hot spots” and thus reduce the programming energy required to blow the fuse. FIG. 4 illustrates a meander shaped resistive element  68  coupled between two electrodes  61 , 62 . The meander bends  64 ,  65  are likely spots of fuse rupture. Dashed line  63  represents current flow which is concentrated at the bends adding to heat generation and rupture. 
     FIGS. 5 and 6 illustrate other fuse/antifuse geometries that take advantage of current crowding effects. These fuses or antifuses  70 , 80  include a “U” or “M” shaped region that at least in part include a channeled resistive element  78 , 88 . 
     The curve of the U or M provides the meander current crowding effect discussed above. In addition, regions  74 ,  84  are configured to form a channel (generally centered in the bend) that further increases current crowding and thus results in more rapid and efficient fuse breakdown. FIG. 5 also shows electrodes  71 , 72  and current path  73 , while FIG. 6 similarly shows electrodes  81 , 82  and current path  83 . 
     The fuse geometries of FIGS. 4-6 may be used in antifuse  30 . 
     While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.