Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-08-14
2004-10-12
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S765010
Reexamination Certificate
active
06803777
ABSTRACT:
BACKGROUND OF THE INVENTION
The development of advanced integrated circuit devices and architectures has been spurred by the ever increasing need for speed. For example, microwave, fiber optical digital data transmission, high-speed data acquisition, and the constant push for faster digital logic in high speed computers and signal processors has created new demands on high-speed electronic instrumentation for testing purposes.
Conventional test instruments primarily include two features, the integrated circuit probe that connects the test instrument to the circuit and the test instrument itself. The integrated circuit probe has its own intrinsic bandwidth that may impose limits on the bandwidth achievable. In addition, the probe also determines an instrument's ability to probe the integrated circuit due to its size (limiting its spatial resolution) and influence on circuit performance (loading of the circuit from its characteristic and parasitic impedances). The test instrument sets the available bandwidth given perfect integrated circuit probes or packaged circuits, and defines the type of electric test, such as measuring time or frequency response.
Connection to a test instrument begins with the external connectors, such as the 50 ohm coaxial Kelvin cable connectors (or APC-2.4). The integrated circuit probes provide the transitions from the coaxial cable to some type of contact point with a size comparable to an integrated circuit bond pad. Low-frequency signals are often connected with needle probes. At frequencies greater than several hundred megahertz these probes having increasing parasitic impedances, principally due to shunt capacitance from fringing fields and series inductance from long, thin needles. The parasitic impedances and the relatively large probe size compared to integrated circuit interconnects limit their effective use to low-frequency external input or output circuit responses at the bond pads.
Therefore, electrical probes suffer from a measurement dilemma. Good high-frequency probes use transmission lines to control the line impedance from the coaxial transition to the integrated circuit bond pad to reduce parasitic impedances. The low characteristic impedance of such lines limits their use to input/output connections. High-impedance probes suitable for probing intermediate circuit nodes have significant parasitic impedances at microwave frequencies, severely perturbing the circuit operation and affecting the measurement accuracy. In both cases, the probe size is large compared to integrated circuit interconnect size, limiting their use to test points the size of bond pads. Likewise sampling oscilloscopes, spectrum analyzers, and network analyzers rely on connectors and integrated circuit probes, limiting their ability to probe an integrated circuit to its external response. For network analysis, a further issue is de-embedding the device parameters from the connector and circuit fixture response, a task which grows progressively more difficult at increasing frequencies.
With the objective of either increased bandwidth or internal integrated circuit testing with high spatial resolution (or both) different techniques have been introduced. Scanning electron microscopes or E-beam probing uses an electron beams to stimulate secondary electron emission from surface metallization. The detected signal is small for integrated circuit voltage levels. The system's time resolution is set by gating the E-beam from the thermionic cathodes of standard SEM'S. For decreasing the electron beam duration required for increased time resolution, the average beam current decreases, degrading measurement sensitivity and limiting practical systems to a time resolution of several hundred picoseconds. Also, SEM testing is complex and relatively expensive.
Valdmanis et al., in a paper entitled “Picosecond Electronics and Optoelectronics”, New York: Springer-Verlag, 1987, shows an electro-optic sampling technique which uses an electrooptic light modulator to intensity modulate a probe beam in proportion to a circuit voltage. Referring to
FIG. 1
, an integrated circuit
10
includes bonded electrical conductors
12
fabricated thereon whereby imposing differential voltages thereon gives rise to an electric field
14
. For carrying out a measurement an electro-opti needle probe
16
includes an electro-optic tip
18
(LiTaO
3
) and a fused silica support
20
. A light beam incident along path
22
is reflected at the end of the electro-optic tip
18
and then passes back along path
24
. An electric field
14
alters the refractive index of the electro-optic tip
18
and thereby alters the polarization of the reflected light beam on the exit path
24
, which thus provides a measure of the voltages on the conductors
12
. Unfortunately, because of the proximity of the probe
16
to the substrate
10
capacitive loading is applied to the circuit, thereby altering measurements therefrom. In addition, it is difficult to position the probe
16
in relation to the conductor because the probe
16
and circuit
10
are vibration sensitive. Also, the measurements are limited to conductors
12
on or near the surface of the circuit
10
. Further, the circuit must be active to obtain meaningful results and the system infers what is occurring in other portions of the circuit by a local measurement
Weingarten et al. in a paper entitled, “Picosecond Optical Sampling of GaAs integrated Circuits”, IEEE Journal of Quantum Electronics, Vol. 24, No. 2, February 1988, disclosed an electro-optic sampling technique that measures voltages arising from within the substrate. Referring to
FIG. 2
, the system
30
includes a mode-locked Nd:YAG laser
32
that provides picosecond-range light pulses after passage through a pulse compressor
34
. The compressed pulses are passed through a polarizing beam splitter
36
, and first and second wave plates
38
and
40
to establish polarization. The polarized light is then directed at normal incidence onto an integrated circuit substrate
42
. The pulsed compressed beam can be focused either onto the probed conductor itself (backside probing) or onto the ground plane beneath and adjacent to the probed conductor (front-side probing). The reflected light from the substrate is diverted by the polarizing beam splitter
36
and detected by a slow photo diode detector
44
. The photo diode detector is also connected to a display
46
.
A microwave generator
48
drives the substrate
42
and is also connected to an RF synthesizer
50
, which in turn is connected to a timing stabilizer
52
. The pulse output of the laser
32
is likewise connected to the timing stabilizer
52
. The output of the stabilizer
52
connects back to the laser
32
so that the frequency of the microwave generator
46
locks onto a frequency that is a multiple of the laser repetition rate plus an offset. As a consequence, one may analyze the electric fields produced within the integrated circuit as a result of being voltage drive, thus providing circuit analysis of the integrated circuit operation. In essence, the voltage of the substrate imposed by the microwave generator
48
will change the polarization in the return signal which results in a detectable change at the diode detector
44
.
Referring to
FIGS. 3A and 3B
, the locations along the incident beam are designated a, b, c (relative to the “down” arrow), and designated along the reflected beam as d, e, and f (relative to the “up” arrow), and the intensity modulated output signal is designated as g. The corresponding states of polarization exhibited in the measurement process are shown in the similarly lettered graphs of FIG.
3
B. At location a of
FIG. 3A
, the polarizing beam splitter
36
provides a linearly polarized probe beam (as shown in graph a of
FIG. 3B
) that is passed through the first wave plate
38
, which is a T/2 plate oriented at 22.5 degrees relative to the incident beam polarization, so as to yield at location b the 22.5 degree elliptically polarized beam shown in graph b of FIG.
3
B). The beam then
Pfaff Paul
Russell Kevin L.
Chernoff Vilhauer McClung & Stenzel LLP
Cuneo Kamand
Nguyen Trung Q
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