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The minute signals from the individual cantilevers are read-back,
filtered, and converted from analog to digital signals by the analog
front-end (AFE). The large number of channels requires integration
of the electronics in a custom CMOS chip*
The figure at right shows a chip micrograph of an AFE chip that
includes 8 read-channels. For a fully functional prototype, the
write-functionality, dedicated servo-channels, digital interfaces,
and test capability have to be added. The block-diagram of the complete
AFE-chip is shown in the next figure. The design of the AFE requires
accurate device models for the cantilever. Based on the results
obtained from accurate finite-element modeling (FEM) simulations
and analytical models, we are developing efficient models that can
be used to simulate large arrays of cantilevers together with the
AFE circuitry in a unified environment.
The large number of cantilevers (e.g., 4096 cantilevers with three
connections each) make it impossible to use traditional bondwires
to interconnect the micromachined cantilever array to the interface
electronics. Therefore, we have developed a wafer-level interconnect
technology that transfers the cantilever onto the AFE chip and uses
the small feature size of the chip's last metallization layer to
connect the cantilevers to the signal acquisition circuitry.
*CMOS: complementary metal-oxide-semiconductor. CMOS is the predominant
technology used to fabricate modern microprocessors and DRAM-chips.
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IBM Research
