Frequently Asked Questions







Microfabrication describes a whole wafer process for the fabrication of micron sized structures, devices and circuits. Such technologies originally derive from the semiconductor industry for the production of integrated circuits and have evolved to realize micro mechanical systems (MEMS) for rf, sensor, biological and other applications. Some of the many advantages of microfabricated over hand-assembled micro structures include greatly increased accuracy in control of feature size and alignment, ability to realize much smaller feature sizes, improved uniformity across batches of the fabricated structures, and the ability to intimately integrate circuit elements with the mechanical design and characteristics of the substrate material. DMPI has taken advantage of its long standing expertise in microfabrication and THz devices & systems to develop a scalable approach of micromachined probe fabrication.
A millimter and submillimeter waveguide is a rectangular metal structure that "guides" electromagnetic waves where the given waveguide geometry will determine the cutoff frequency below which radiation will not propagate down the waveguide. Within a waveguide the electric field is normal to the wider wall and the magnetic field line is normal to the shorter wall. In a split block, the waveguide structure is cut along the E plane (i.e. through the longer wall) in order to minimize the effect on the radiation once the block is closed since the current flow across the split of such a block is negligible. The split in the block is typically desired in order to insert a device chip between the two planes of the block. The DMPI microfabricated Si probe chip is mounted and clamped in a waveguide split block allowing for drop-in replacement of the probe chip without needing replacement of the entire block module
At rf and THz frequencies, unlike at low (or dc) frequencies, we view connections to a circuit as ports composed of transmission lines (not simple wires). These transmission lines support waves traveling into and out of the circuit. Scattering parameters (S-parameters) describe the frequency dependant electrical behavior of the network under steady state small signal traveling wave currents and voltages. Given that a network can have any number of ports, the measurement of the reflected wave at the input port, or the transmitted wave at the Nth port depends on the state of all the remaining ports. To obtain the S-parameters of such a network, the unused ports are terminated (matched) with the characteristic impedance of the ports transmission lines. For a simple two port network, the scattering parameters can be described by a 2x matrix where S11 is the reflection at port 1 with port 2 properly terminated, S21 is the transmission coefficient from port 1 to port 2, etc.
DMPI metal fixtures and Si probe tips are relatively robust. Click on the DMPI probe assembly to the right and see a movie of a DMPI WR1.5 probe being lowered into contact, and then purposefully furthered lowered until the probe assembly fixture actually bottoms out on the wafer. Even in such an extreme case, the probe tip survives this over probing force. Note, in the video you are seeing both the probe and its reflection on the wafer surface For Repairs, unless the robust metal block itself has been damaged, the probe chip can be replaced repeatedly by DMPI with typical performance as new.
Block Video    
      Click on block to see video (mov format) of probing
(click here for avi format)












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