LTCC Ceramic Calorimeter

Although LTCC ceramic can be used for a huge number of applications, one promising application is using ceramic to fabricate calorimeter devices for biodetection. The focus of my research this summer is to create such a calorimeter. Because circuitry can be screen printed on LTCC ceramic, the material lends itself well to calorimeter fabrication. This has already been demonstrated by Missal in [1]. He created a differential scanning calorimeter using LTCC materials.The importance of using LTCC materials over conventional materials is that LTCC can be used to fabricate very small devices. Large analyzers can be redesigned and produced using LTCC tape.

The goal of my summer research project is to produce a simple cost-effective biodetector using a simple heat sensor. Many biodetectors use color or size to differentiate and measure molecules. The alternative approach I will be using is to measure an exothermic reaction with a heat sensor. The temperature data from this sensor can hopefully used to accurately measure the concentration of the reactants.

Figure 1. Exposed LTCC temperature sensor.

The fundamental component used in my heat sensor is a thermistor. A thermistor is a resistor with extreme temperature sensitivity. A very small change in temperature will result in a massive change in resistance. Because I am using a printable thermistor material, I can experiment with different shapes to optimize sensitivity. Currently I am using a design that was developed by my mentor Dr. Rich Eitel (Figure 1), but I am working on a new design that will allow me to test multiple thermistors using the same screen (Figure 2). In order to screen print, a new screen must be made for each design. In Figure 1, the model uses two screens, one for the electrodes and one for the thermistor material. Screen printing works by squeezing a small amount of ink through a tight mesh. 

Figure 2.  Draft of new screen designs. Each design is for
one 3"x3" sheet of LTCC ceramic and will make 2 chips.

I have already run one test on the current model and I currently fabricating several more chips. I tested the chip in ice water to get a baseline for noise. From the data analysis, I determined that I should be able to measure temperature fluctuations as low as .01 degrees Celsius with the thermistors. My new screen designs are still in progress, Figure 2 is only my first draft, and I plan on making several improvements before we make the screens. Not only will the new design allow for testing three resistors with the same screen, it will also have three sensors instead of two. I am also working on designs for wells to contain reactions and lay over the thermistors (Figure 3). The final device will have microfluidic channels leading into wells on top of each thermistor.

Figure 3. Draft of channel and well design. 

References

[1]    W. Missal, J. Kita, E. Wappler. Miniaturized Ceramic Differential Scanning Calorimeter with Integrated oven and Crucible in LTCC Technology. Sens. Actuators A: Phys., 172 (2011), pp. 21-26