Trench isolation for reduced cross talk

Abstract

A starting substrate in the form of a semiconductor wafer (1) has a first side and a second side, the sides being plane-parallel with respect to each other, and has a thickness rendering it suitable for processing without significant risk of being damaged, for the fabrication of combined analogue and digital designs, the wafer including at least two partitions (A1, A2; DIGITAL, ANALOGUE) electrically insulated from each other by insulating material (2; 38; 81; L) extending entirely through the wafer. A method for making such substrates including etching trenches in a wafer, and filling trenches with insulating material is also described.

Description

FIELD OF THE INVENTION[0001]The present invention relates to design of micro electronic devices where e.g. both analogue and digital units are to be located in close proximity on substrates such as micro chips. In particular it relates to means and methods for eliminating or at least reducing so called cross-talk between analogue / digital components on the same substrate.BACKGROUND OF THE INVENTION[0002]When analogue and digital components are located on the same substrate in close proximity, such as is the case for ASIC devices, inevitably there will occur so called cross-talk between these components.[0003]Capactive crosstalk can e.g. occur when digital signals are run near analog signals, the capacitance between the lines can cause the lines to couple and the signals become blurred due to coupling through the substrate underneath.[0004]This problem can be eliminated by running the analog signals in a separate routing area than the digital, and by putting grounding shields between ...

AI Technical Summary

Problems solved by technology

If this ground differs from the originator of the signal, this will cause voltage differences at the rate of the bits.

Some of the major problems induced by digital to analog and analog to analog cross talk are (1) high speed digital clocks cause severe interference with RF or IF front ends; (2) in digital portables, time-division-multiple-access (TDMA) may be used and power on / off cycles happen fairly frequently, causing additional transient noise on the power and ground planes; (3) in frequency division duplex systems, as well as in pixel based imaging devices, high-power transmit signals cause interference with weak receive signals since separation by filters is limited; (4) the leakage of the amplifier output to the input may cause the amplifier to oscillate.

The physical interface between an IC and its environment is the IC package, and its performance is severely tested by the high speed and high frequencies encountered in wide-bandwidth systems.

The latter is of course limiting on the possibilities to reduce component size, which is disadvantageous.

The general problem with this type of solution is that trenches must be narrow enough to be able to be filled.

Such thin wafers are not possible to use as starting substrate.

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