Relevant publications:

A Microtransceiver for UHF Proximity Links Including Mars Surface-to-Orbit Applications
Kuhn, W., Lay, N. E.,Grigorian, E.; Nobbe, D.; Kuperman, I.; Jeon, J.; Wong, K.; Tugnawat, Y.; He, X.
Proceedings of the IEEE, Vol. 95, Issue 10, pp. 2019-2044, Oct 2007

A UHF Proximity Micro-Transceiver for Mars Exploration
Kuhn, W.; Lay, N.; Grigorian, E.
2006 IEEE Aerospace Conference, 4-11 March 2006

Low Temperature Performance of COTS Electronic Components for Future Mars Missions
Y. Tugnawat; and W. Kuhn
12th NASA Symposium on VLSI Design, Oct 4-5, 2005

A Low-Volume, Low-Mass, Low-Power UHF Proximity Micro-Transceiver for Mars Exploration
W. Kuhn; N. Lay; and E.Grigorian
12th NASA Symposium on VLSI Design, Oct 4-5, 2005

Low Temperature Performance of Commerical-Off-The-Shelf (COTS) Electronic Components for Future Mars Missions
YOGESH TUGNAWAT M.S., Kansas State University, 2004


Cryogenic Testing

In order to design communication circuits that can function in the extreme temperatures of other planets (e.g. Mars), cryogenic testing has been used at K-State to understand analog/RF circuitry behavior at temperatures as low as -100° C. Specifically, there are two primary considerations for low-temperature operation:

To simulate these temperatures, cryogenic testing has been conducted at K-State, in a custom cryogenic facility described here.  Various circuits and devices are cooled to very low temperatures via liquid nitrogen.  Below, a former graduate student can be seen preparing to cool his DUT:



Parametric Drift

Several design parameters will shift in value as ambient temperatures are decreased from 25° C (room temperature) to -100° C.  For example, the TCXO on the Mars microtransceiver board was cooled to -100° C to observe its changes in frequency.  A plot of this data is shown here:


The characteristic curves for n-type and p-type FETs are also dependent on temperature.  During the same Mars microtransceiver project, data was taken to plot drain current vs drain-source voltage over a wide range of temperatures for both genders of FETs.  These graphs are seen below:

rnfet rpfet

Other parameters, such as the sheet resistance of various substrates inside an IC, can also change in extremely low temperatures.  Observe the following graph, which shows the percent change of the resistance for many different materials that compose a FET:


The frequency drift of a VCO, due to low temperatures, can be seen in the animation below:


Test Setup

Below are some images of the setup in the cryogenics lab.

cryotestic    This image displays a demoboard
    prepared to be submerged in a case
    where it is to be cooled to temperatures
    well below 0° C.






setup1    After placing the demoboard in the case,
    it is covered with a separate insulator and
    the case's lid is screwed on.









setup3    At this point the outer box of the
    apparatus is placed into position
    and data can be taken from the







setup4    Here the ambient temperature of the
    apparatus has reached -91.7° C.












Taking Data Directly off of Silicon Wafers

Another method of measuring RFIC performance characteristics employed in the cryogenic testing facility is probing actual silicon wafers themselves, which contain many instances of test ICs on its surface.  The wafer can also be cooled down to extremely low temperatures, allowing for accurate low-temperature measurements.

wafer1    Here a silicon wafer is under test.
    The tips of the probes used to take
    the actual measurements are much
    too small to be seen clearly at this scale.









wafer2    Using a microscope, the tip of the
    probe can be seen.  These terminals
    are in contact with the dye of the test IC,
    which is printed many times over on the
    silicon wafer.









wafer3    Upon being cooled to a very low temperature,
    it can be seen that the silicon wafer becomes
    covered in ice, as well as some of the
    instruments used to take data.  However,
    the apparatus is designed to still allow the
    probes to take unobstruced test measurments,
    despite the presence of ice.








The Cryogenics Lab in Action

The following videos show graduate students and professors at work in the cyrogenic testing facility.

bullet Accessing the coolant I
Accessing the coolant II
Reaching 100° Kelvin