Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-10-20
2003-10-21
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S754120, C250S341400
Reexamination Certificate
active
06636056
ABSTRACT:
FIELD
The present invention relates to integrated circuits, and more particularly, the present invention relates to testing integrated circuits.
BACKGROUND
Integrated circuits, such as processors and application specific integrated circuits, are routinely fabricated from millions of signal sources, such as logic gates. The interconnections that couple logic gates together are called nodes. One or more logic gates may be coupled to a node. During the operation of a digital integrated circuit, the nodes carry signals that have positive and negative logic levels. In testing a digital integrated circuit, input signals are provided to the integrated circuit and the signals at each node are monitored to determine whether the circuit is operating correctly. Specifically, for a digital integrated circuit, each node must be capable of assuming a positive logic level and a negative logic level. For nodes in a digital integrated circuit not connected to an output pad, the positive and negative logic levels cannot be measured directly. Therefore, testing the operation of a particular node in an integrated circuit often requires identifying a sequence of input signals to the integrated circuit that causes a change in the logic level at the particular node and that also causes a corresponding change in the logic level at an output pad not directly connected to the particular node. Unfortunately, in many integrated circuits some nodes are not testable in this way because a pattern of signals does not exist for changing the logic level of a particular node and having the change in logic level reflected at an output pad not directly connected to the particular node.
Integrated circuits can be fabricated with optical switching devices providing backside optical input/output (I/O). An integrated circuit is typically formed on one side of a substrate. The side of the substrate opposite from the side on which the integrated circuit is typically formed or located is the backside of the substrate. Backside optical I/O is provided by optical switching devices fabricated on the backside of a substrate. Optical switching devices do not require output pads in order to couple output signals to circuits external to the integrated circuit and the die. The output signals from optical switching devices can be coupled to circuits external to a die through an optical beam. Optical switching devices can also be connected to nodes in the integrated circuit. Specifically, optical switching devices can be connected to nodes that are not testable through I/O pads.
FIG. 1
is an illustration of a prior art system
100
for testing a signal source
102
using an optical switching device
104
. The optical switching device
104
may be fabricated from a pn-junction or a metal-oxide semiconductor (MOS) gate. If device
104
is fabricated from a pn-junction and a laser beam
106
is coupled to the pn-junction through the backside of silicon die
108
, then the reflected beam
110
is produced at the pn-junction. If an electrical signal from signal source
102
is applied to the pn-junction while laser beam
106
is coupled to the pn-junction, then reflected beam
110
is modulated by the electrical signal and includes the information contained in the electrical signal. Similarly, if the optical switching device
104
fabricated from a MOS gate having a charge layer and the laser beam
106
is coupled to the charge layer through the backside of silicon die
108
, then the reflected beam
110
is generated at the charge layer. If an electrical signal from signal source
102
is applied to the charge layer while laser beam
106
is coupled to the charge layer, then reflected beam
110
is modulated by the electrical signal and includes the information contained in the electrical signal. For optical switching device
104
, reflected beam
110
is converted to detected signal
114
at an output port of detector
116
.
Unfortunately, several problems arise in attempting to recover the information contained in reflected beam
110
. First, the modulation of reflected beam
110
is small, so reflected beam
110
has a low signal-to-noise ratio, which decreases the probability of correctly detecting the information contained in reflected beam
110
. Second, since reflected beam
110
has a low signal-to-noise ratio, detected signal
114
, which is generated at detector
116
from reflected beam
110
, is sensitive to the alignment of reflected beam
110
with detector
116
. Any misalignment between reflected beam
110
and detector
116
decreases the probability of correctly detecting the information contained in reflected beam
110
. Third, since the refractive index of silicon varies with temperature, temperature changes in the integrated circuit cause the direct current component of the signal generated at detector
116
to drift. Drift at detector
116
also decreases the probability of correctly detecting the information contained in reflected beam
110
and is a significant problem in attempting to decode phase encoded information from reflected beam
110
. Finally, each of the above described problems increases the difficulty of successfully testing a logic node through a single backside I/O device.
For these and other reasons there is a need for the present invention.
REFERENCES:
patent: 5872360 (1999-02-01), Paniccia et al.
patent: 6049639 (2000-04-01), Paniccia et al.
patent: 6052498 (2000-04-01), Paniccia
patent: 6072179 (2000-06-01), Paniccia et al.
patent: 6075908 (2000-06-01), Paniccia et al.
patent: 6201235 (2002-03-01), Takeuchi et al.
patent: 6232765 (2002-05-01), Takeuchi et al.
Cuneo Kamand
Nguyen Jimmy
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