Miniaturized thin-film magnetic field probe with high spatial resolution for LSI chip measurement

Abstract

Abstraec-It is important to obtain the absolute value of current flowing through each power line on P chip of large-scale integrated &SI) circuits by measurement because this current on an LSI chip is regarded as conductive noise. We have developed a thin-film magnetic field probe that has spatial resolution high enough to obtain the absolute value of high-frequency power current on an LSI chip. Spatial resolution was enhanced by miniaturizing the shielded loop coil, the detection part of the probe. The outer size of the new coil is 50 x 22 pm. In taking measurements with the new probe over a 60-pm-wide microstrip line used as a device under test @UT), we obtained a 6dB decrease point of40 pin, which indicates the spatial resolution of the probe. This value is comparable to the typical width of power lines on an LSI chip, around 50 pm and is less than half that of our conventional probes, around 90 pm. In measurements with the new probe over an LSI chip, we obtained such a fine magnetic near-field distribution that the magnetic fields generated from the lines on the chip were separated. On-chip decoupling was also confirmed by using the new probe. The new probe enables direct verification of a circuit design for suppressing electromagnetic interference (EMI), while conventional coarse mapping of the magnetic near-field cannot be used to evaluate such conductive noise.Kqwords-component: thin-film magnetic Jield probe: magnetic near-field measurement; high spofial resolufion; ntirrosrrip line; LSI chip I. I~TRODUCTIONAs a method for evaluating electromagnetic interference (EMI), magnetic near-field measurement has been utilized for magnetic near-field mapping, contact-less current measurement, and so on. In measurement at the LSl chip level, the purpose of this mapping is usually to evaluate the electromagnetic emission radiated directly from the LSI chip [l]. Conventional mappings on LSI chips are too coarse compared with the width of power lines on the LSI chips. On the other hand, it is important to obtain the absolute value of current flowing through each power line on an LSI chip, because this current is considered to affect EMI as well as direct electromagnetic emission from an LSI chip. This current is considered to couple or conduct to other power circuits outside the LSI, leading to driving cables or power-ground planes on printed circuit boards (PCBs). There is also a possibility that this current is the source of the degradation of signal integrity (SI) or power integrity (PI). If the highfrequency current flowing through each power line on an LSI could be obtained from magnetic near-field measurement along with calibration, the LSI circuit design for EMI suppression could be directly verified by tracing high-frequency current paths on the LSI chip, verifying on-chip decoupling circuits, and so on. Current measurement could also be used to verify simulation models of LSI power circuits. To obtain this current value, however, magnetic field probes are required to have much higher spatial resolution in com...

Response of a magnetic loop probe to the current and voltage on a microstrip line

“…In both cases, we can observe that at low frequencies, when the loop inductance can be neglected compared to Ω 50 , C I rises with 20dB per decade, whereas the curve becomes flat at higher frequencies. This effect is caused by the voltage division described by (6). The presented results can be used to decide whether a given voltage on the microstrip line will be detrimental to the output signal of the probe, which is supposed to be determined only by the trace current in the ideal case.…”

“…The behavior of the probe in its typical configuration must be investigated instead. Electric field rejection of a miniature shielded magnetic loop probe above a shorted microstrip trace has been demonstrated in [5], [6], making use of the standing wave pattern of the trace current. In this paper, a method to evaluate magnetic and electric field coupling into a simple magnetic loop probe positioned above a microstrip line is presented.…”

Magnetic near-field probe for GHz band and spatial resolution improvement technique

“…Fluctuation over 6GHz for V H is attributed mainly to impedance miss matching around at connector or pad pattern on probe. To improve spatial resolution, it is necessary to lower effective measurement height h eff and achieved with physical miniaturization of loop element typically [7,8]. In the meanwhile, detection range for magnetic field has trade-off with spatial resolution related to loop size and optimized probe size for each target should be fabricated and utilized respectively.…”

Modeling of Noisy EM Field Propagation Using Correlation Information

“…The magnetic current is the source of the dual vector potential , given by (38) With (39) we obtain the magnetic field excited from as (40) where is the Green's dyadic relating the excited electric field to the vector potential , and the integration is extended over the whole volume , where is nonvanishing. is given as (41) From (40), we obtain with (42) the magnetic field excited from as (43) where is the Green's dyadic relating the excited magnetic field to the vector potential , and the integration is extended over the whole volume , where is nonvanishing. is given as…”