# Presentation: 201176

## DESIGN AND FABRICATION OF MJTCs ON QUARTZ SUBSTRATES AT NIST

- L. Scarioni , T. E. Lipe  and J. R. Kinard

**Universidad de Carabobo****Facultad Experimental de Ciencias y Tecnología **
**Valencia Venezuela**

## NIST – SANDIA NATIONAL LABORATORIESTHIN-FILM MULTIJUNCTION THERMAL CONVERTER 

- Silicon Frame

- Thermocouples

- Heater

- Membrane

**Notes:**
The standard PTB-PJMTC is fabricated on a silicon chip with a thin dielectric membrane. A thin-film bifilar heater and a up to 100 thermocouples are sputtered on an Si3N4/SiO2/Si3N4 sandwich membrane. The hot junctions of the thermocouples are located along the bifilar heater and the cold junctions are on he silicon frame acting as a heat sink. The window is anisotropically etched into the silicon chip.

## FABRICATION OF THE QUARTZ-MJTCs 

**Micromachining of Quartz**
- At-cut monocrystalline quartz wafer.
- 76 mm diameter, 250 mm thickness.
- Quartz etchant: mixture of hydrofluoric acid, HF, and ammonium fluoride, NH4F in proportions HF:NH4F = 2:3. The etch rate  is 20 m/h for a temperature of 60 °C.
- Au layer of 100 nm thickness evaporated on a 10 nm Cr layer as mask material for etching. Etching patterns for the membrane were defined  by standard photolitographic techniques.

- Quartz Wafer

- Quartz Membrane

**Notes:**
For the construction of the new thermal-converter, we have used the AT-cut monocrystalline, because with this cut we obteined a smooth surface.
The wafer has a diameter of 76 mm and  a thickness of 250 micrometers.
The quartz etchant was a mixture of hydrofluoric acid, HF and amonium fluoride, NH4F in proportions HF:NH4F = 2:3. The etch rate for this concentration is around 20 m/h for a temperature of 60°C.
An Au layer of 100 nm thickness evaporated on a 10 nm Cr layer was used as mask material for etching. The etching patterns for the membrane were defined in the mask by standard photolitographic techniques and carefully aligned at direction rotated by 24° against the crystallographic x-axis.
Thi figue show that the etching along the crystal axis results in a reproucible geometry of the window with a quartz membrane of a few micrometers thickness.

## Membrane Fabrication

**Membrane Fabrication**

**Etching Beakers**

**Wafer Showing Membranes**

## COAXIAL MJTC ON A QUARTZ CRYSTAL CHIP 

- Heater

- Thermocouples

- Membrane
- Boundary

- Ceramic
- Mount

- Die is 6 mm by 7 mm.

**Notes:**
The structure of the bifilar heater and the thermocouples was fabricated using the standard photolithographic process and wet etching.  The figure shows a photo of the thin-film MJTC chip on a quartz crystal chip. 

## BIFILAR MJTC ON A QUARTZ CRYSTAL-CHIP 

**BIFILAR MJTC ON A QUARTZ CRYSTAL-CHIP**

- Heater

- Thermocouples

- Ceramic
- Mount

- Die is 6 mm by 7 mm.

- Membrane
- Boundary

## THE SIMULATION MODEL

- Change of the real part of the heater impedance _*Z*_  with frequency

**Notes:**
To calculate the ac-dc transfer differences of the new thermal converter a model of the PJMTC was developed. This model includes the contribution of ac-dc differences arising from:

The distributed model considers the heater inductance, capacitive coupling between the two halves of the heater, capacitive coupling between the heater and the thermocouples and the power losses in the quartz substrate. The PMJTC heater is modeled as a lossy transmission line of ten elemens. The model is built from lumped elements i.e. resistances, capacitances, inductances and conductances. 

## CALCULATED VALUES FOR DIFFERENTHEATER RESISTANCES

- 1

- 1

- 0

- 1

- 0

- 0

- F

- r

- e

- q

- u

- e

- n

- c

- y

- i

- n

- M

- H

- z

- R

- =

- 2

- 5

- 0

- 

- R

- =

- 5

- 0

- 0

- 

- R

- =

- 1

- 0

- 0

- 0

- 

**CALCULATED VALUES FOR DIFFERENT****HEATER RESISTANCES**

- 0

- -500

- -1000

- -1500

- -2000

- Ac-dc Difference in μV/V

##  HOUSING WITH INTEGRATED Tee FOR THE CALCULABLE QUARTZ-MJTC 

- Signal
- Input

- Defined
- Signal
- Output

- Thermo-
- Couple
- Output

## MEASURED AC-DC DIFFERENCESFOR COAXIAL QUARTZ MJTC 

- 1

- 1

- 0

- 1

- 0

- 0

- 0

- Ac-dc differences in %

- F

- r

- e

- q

- u

- e

- n

- c

- y

- i

- n

- M

- H

- z

- S

- i

- m

- u

- l

- a

- t

- i

- o

- n

- M

- e

- a

- s

- u

- r

- e

- m

- e

- n

- t

- s

**MEASURED AC-DC DIFFERENCES****FOR COAXIAL QUARTZ MJTC*** *

- -1

- -2

- -3

- -4

## MEASURED AC-DC DIFFERENCESFOR BIFILAR QUARTZ MJTC

- 1

- 1

- 0

- 1

- 0

- 0

- Ac-dc differences in %

- F

- r

- e

- q

- u

- e

- n

- c

- y

- i

- n

- M

- H

- z

- S

- i

- m

- u

- l

- a

- t

- i

- o

- n

- M

- e

- a

- s

- u

- r

- e

- m

- e

- n

- t

- s

**MEASURED AC-DC DIFFERENCES****FOR BIFILAR QUARTZ MJTC**

- 0

- -1

- -2

- -3

- -4

- -5

- -6

## PRESENT ACTIVITIES

- New set of converters, with smaller heater resistances (≈ 830 Ω) is being fabricated.
- Thicker thermocouple depositions are also being used, in order to reduce the thermocouple resistances from about 40 kΩ to less than 20 kΩ.

## CONCLUSION

- A new generation of MJTCs on crystal quartz chips and membranes are being fabricated at NIST.
- The results of the simulation show that the use of crystalline quartz allows significant reductions in the standard uncertainties and the ac-dc differences of the MJTCs in the frequency range from 100 kHz to 100 MHz.

## ACKNOWLEDGMENT

- 	Research performed in part at the NIST Center for Nanoscale Science and Technology.
- 	Funded as part of CCG
- 	Project Number 546.

## Thank you for your attention 

- L. Scarioni , T. E. Lipe  and J. R. Kinard