Abstract:
According to one embodiment an apparatus is disclosed. The computer apparatus includes a first integrated circuit (IC) and a second IC. The second IC includes a soft error rate (SER) immune component and a SER component to detect radiation that could result in soft errors at logic at the first IC.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to integrated circuits; more particularly, the present invention relates to the detection of soft errors in integrated circuits.  
       BACKGROUND  
       [0002]     Currently, expensive radiation detectors are required to detect ambient radiation. These radiation detectors are constructed using Geiger-Mueller tubes. These tubes are quite fragile, and thus are easily broken. Moreover, the radiation detectors are relatively large and consume a large magnitude of power. Therefore, the detectors are not portable.  
         [0003]     In the world of integrated circuits (ICs), transistors have sizes in the sub-micron range. Such small transistors are more sensitive to cosmic (neutrons) and alpha particle strikes. Consequently, particle hits to the silicon on which the transistors are fabricated can literally change the state of the transistor. For example, a latch holding a  0  value may be changed to a 1 value. This phenomenon is referred to as soft error.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     The present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention. The drawings, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only.  
         [0005]      FIG. 1  illustrates one embodiment of a computer system;  
         [0006]      FIG. 2  illustrates one embodiment of a radiation detector;  
         [0007]      FIG. 3  illustrates a graph of one embodiment of a typical Alpha strike; and  
         [0008]      FIG. 4  illustrates a graph of one embodiment of a typical Neutron strike.  
     
    
     DETAILED DESCRIPTION  
       [0009]     A mechanism for detecting radiation is described. Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.  
         [0010]     In the following description, numerous details are set forth. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.  
         [0011]      FIG. 1  is a block diagram of one embodiment of a computer system  100 . Computer system  100  includes a central processing unit (CPU)  102  coupled to bus  105 . In one embodiment, CPU  102  is a processor in the Pentium® family of processors including the Pentium® II processor family, Pentium® III processors, and Pentium® IV processors available from Intel Corporation of Santa Clara, Calif. Alternatively, other CPUs may be used.  
         [0012]     According to one embodiment, bus  105  is a front side bus (FSB) that communicates with a memory control hub (MCH)  110  component of a chipset  107 . MCH  110  includes a memory controller  112  that is coupled to a main system memory  115 . Main system memory  115  stores data and sequences of instructions and code represented by data signals that may be executed by CPU  102  or any other device included in system  100 . In one embodiment, main system memory  115  includes dynamic random access memory (DRAM); however, main system memory  115  may be implemented using other memory types.  
         [0013]     According to one embodiment, MCH  110  is coupled to an input/output control hub (ICH)  140  via a hub interface. ICH  140  provides an interface to input/output (I/O) devices within computer system  100 . For instance, ICH  140  may be coupled to a detector  150 . In one embodiment, detector  150  is coupled to ICH  140  via a serial link. However, one of ordinary skill in the art will appreciate that other links (e.g., optical, flip-chip, die-stack, etc.) may be implemented.  
         [0014]     According to one embodiment, detector  150  detects radiation conditions within computer system  100  that may lead to soft error at ICs within computer system  100 . Particularly, detector  150  may detect various levels of radiation (e.g., alpha, neutron and gamma particle types).  FIG. 2  illustrates a block diagram of one embodiment of detector  150 .  
         [0015]     Referring to  FIG. 2 , detector  150  includes logic arrays  210  and  220 . In one embodiment, logic arrays  210  and  220  are designed to have a significant soft error rate (SER). Normally modern semiconductor structures are designed to be immune to SER. Thus, careful design techniques are used to absorb random alpha particle or neutron strikes and not flip logic states or memory states. However, for detector  150  the opposite is done. Logic arrays  210  and  220  change states if alpha and neutron particles, respectively, strike the diffusion regions.  
         [0016]     Alpha and neutron strikes have different energy transfer profiles in a semiconductor. Logic  210  and  220  take advantage of these separate profiles by being designed to be more sensitive to one type of strike as opposed to the other.  FIG. 3  illustrates a graph of one embodiment of an energy profile for an alpha strike, while  FIG. 4  illustrates a graph of one embodiment an energy profile for a typical neutron strike.  
         [0017]     Since both logic arrays  210  and  220  are more sensitive to a particular type of strike, detector  150  may detect varying amounts alpha or neutron radiation, and thus alert to not only the relative strength of the source of radiation but also to its type. In one embodiment, the SER sensitive parts such as arrays  210  and  220  have large diffusion area exposure, but have low capacitance. In a further embodiment, arrays  210  and  220  include inverters and latches that are asymmetric in drive strengths to further be subject to either alpha or neutron strikes and to be more likely to flip from a given seeded logic state to its opposite.  
         [0018]     In an alternative embodiment, a form of DRAM cell is a good candidate for radiation and SER detection. Therefore, logic arrays  210  and  220  may also be implemented as memory arrays. Further logic arrays  210  and  220  would include few transistors. No special trenches are needed because only parasitic diffusion capacitance is needed, and the refresh rate is controlled to act as a sensitivity control to alpha or neutron strike rates (while being refreshed the cell would tolerate a strike). In a further embodiment, a known fixed pattern is written into the arrays.  
         [0019]     Detector  150  also includes SER immune components. Such components include input/output (I/O) logic  240 , timers/control  250 , control logic  260 , read only memory (ROM)  270 , random access memory (RAM)  275  and non-volatile memory  280 . In one embodiment, on die shielding of the SER immune sections can limit alpha strikes, and careful logic design for the non-SER sensitive areas can limit both alpha and neutron upset to the control sections.  
         [0020]     I/O logic is also included within detector  150 . I/O logic is used to receive input data and to transmit output data. For example, the inputs may include an ON/OFF input and a sensitively selector that would just change the sampling rate of reading the arrays, or the refresh rate of the logic arrays. Likewise outputs may include a modulated audio tone or an LED/LCD display to show some relative dose rate.  
         [0021]     Timers/control  250  control the rate at which logic arrays  210  and  220  are examined. Control logic  260  is implemented to analyze logic arrays  210  and  220  and to determine whether the arrays have been exposed to radiation. According to one embodiment, control logic  260  examines logic arrays  210  and  220  at intervals determined by control logic  260 , as discussed above. Upon examination, control logic  260  compares the recently read known values to those previously stored and determines whether there is a match.  
         [0022]     For the memory array embodiment, if there is not a match between the known values and the examined values, a time varying level of defective bit values are detected. The time varying level of defective bit values are proportional to the level of radiation upset. Similarly, for logic blocks dense logic structures are created that have fixed inputs. Because the design of the structures is known, the combinatorial outputs are also known. By periodically reading the output stages of the structure, a time varying level of defects caused by radiation-induced upset is detected.  
         [0023]     According to one embodiment, control logic  260  is implemented as a CPU. However in other embodiments, control logic  260  is implemented as a very low power and small transistor microcontroller since control logic  260  does not need to operate very fast. ROM  270  stores a simple operating system and constants. In addition, RAM  275  is used to for the upset rate calculations.  
         [0024]     Non-volatile memory  280  stores expected SER array signatures and the calibration results. For example, detector  150  is exposed to, and measures, a known rate source of upset prior to its use. In response, the amount of hits are detected and saved as a constant within detector  150 . Device  150  may be calibrated by known alpha and neutron sources at assembly/test time of the final system.  
         [0025]     In one embodiment, standard CMOS fabrication techniques are used for fabricating the electronic sections within detector  150 . One side benefit of using standard CMOS logic processes is that the SER sensitive arrays, either logic or memory, can be mapped for defects at time of fabrication and such fabrication faults stored in the NV memory as areas to ignore or as the correct background signatures. The manufacturing yield of the device therefore would be much higher than normal semiconductor products, thus lowering the cost of the device even more than normal. No additional error correction circuits would be needed to the SER sensitive array sections.  
         [0026]     Although detector  150  has been described as a separate device within computer system  100 , all of the functions of the radiation detection technique can be integrated into CPU  102 , chipset  107  or any other semiconductor device within computer system  100 . In such an embodiment, the radiation sensitive logic arrays and/or memory arrays can be part of a larger die or system that uses radiation immune controller logic, either in a single die or a stacked die technique.  
         [0027]     Moreover, detector  150  may be implemented as a stand-alone radiation detector separate from a computer system. Such a device is small and light, and operates on a single or double AA battery and last the shelf life of the battery the controller logic would be inactive since most of the time, and the other SER sections would be static and not clocked.  
         [0028]     By using the solid-state approach described here, all of the limitations in the radiation detectors described above are overcome. The solid-state radiation detector can be produced at various sensitivities and feature sets with prices ten times less than previous models. The low cost of these solid-state versions, make such systems available to huge numbers of people not just scientists. Every police, fire, and emergency group could have (or wear) such a device. Homeowners could check for Radon in basements and other structures.  
         [0029]     In addition, the SER application SER helps verify how and when a device should correct faulty data from an SER event. Such a feature could be used to help determine when to gracefully recover from an SER event that could not be on-board corrected.  
         [0030]     Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims which in themselves recite only those features regarded as the invention.