1. Ultrastable Thin Film TiC Resistors for Space Applications
Robert C. Cole1 and Gouri Radhakrishnan2
The Aerospace Corporation
1Parts, Materials and Processes Dept.
Electronics and Sensors Division
May 5, 2010
2 Materials Science Dept.
Space Materials Laboratory

2. Topics of Discussion Thin Film Resistor Problems TiC thin films
Fabrication Details
Testing
Summary

3. Thin Film Resistors - Overview
Thin film resistors are widely used for high performance hybrid microcircuits.
Integral part of the metal interconnect system.
Offer greater design latitude to the circuit designer; can be laser trimmed with high precision and show good stability in hermetic packages.
For RF circuit applications, thin film resistors offer a reduction in electrical circuit parasitics by reducing unwanted inductance and capacitance.
Package size and weight can be significantly reduced using hybrid technology as compared to discrete resistor use on PC boards.
This reduction in weight and increased performance are necessary for meeting today’s Space Systems Requirements.

4. Thin Film Resistors – Status and Problems
The low TCR (Temperature Coefficient of Resistance) of Nichrome (<50 PPM) has made it the material of choice for hybrid microcircuits and resistor networks.
Issues with Nichrome:
Sensitivity to moisture under typical bias loads in circuit applications.
Sensitivity to short duration high power transient voltage pulses. Worst case circuit analysis has predict that resistor failures from these high power pulses can result in system failures.
Tantalum Nitride
Moderate TCR ~ 100 PPM
Good stability to moisture under bias loads
Film properties degrade at temperatures above 125°C

5. Titanium Carbide Thin Films
Poly-Si
SiO2 (2)
SiO2 (1)
Poly-Si (0)
Si3N4 Si
Hybrid pulsed laser deposition and
Si-surface-micromachining process for
integrated TiC coatings in moving MEMS
G. Radhakrishnan , R.E. Robertson, R.C. Cole, P.M. Adams
Appl. Phys. A 77, 175–184 (2003)
Poly-Si (1)
TiC (2)
N+ Poly-Si (0)
SiO2 (1)
Silicon Nitride
TiC (1)
Silicon substrate

6. Titanium Carbide Thin Films
TiC has a very high melting point (3500 K), a high resistance to chemical attack and most importantly low sheet resistivity (100 /sq)
Pulsed Laser Deposition (PLD) Titanium Carbide was incorporated into a standard Silicon/MEMS wafer processing flow.
Excellent adhesion properties were observed to sapphire and silicon substrates.
Readily etched by standard Reactive Ion Etch gases.
The TCR of TiC was calculated to be 76 PPM on sapphire substrates.

7. Fabrication Process Flow

8. Fabrication cont’d Resistor Network Individual Thin-Film TiC Resistor
Final Packaged Resistor Network

9. TiC Resistor Data
Resistor #
Pulse #
Pulse Width (µs)
Voltage (V)
Resistance (kΩ) 4 1 5
250
1.7726
1.7735 10 6
1.7763 15 7
1.7823 20 8
1.8522
300
1.8011
1.8009 2
1.8 3
1.8048
1.8206 25
OPEN
200
1.84
1.8391
1.8384
1.8472 29 30

10. TiC Resistor Network: Post Pulsed Power Testing
Molten Metal
(Gold 5KÅ)
Intact TiC Resistor

11. Pulse Power Testing on TiC Resistor
Initial
Resistance k
After Pulse Power Testing 1
1.79
1.975 2
not there 3
ground 4
1.776
R4*
1.8425 6
1.802
R6*
1.843 8
1.824
1.8228 9 10
1.818
1.8168
* Re-wirebonded and measured

12. TiC Resistor Operation under cw Power

13. TiC Resistor Operation under cw Power
Package 8
Resistor 21 Ri Rf .
1846.9
2271
Run # V
I (mA) R
P (mW)
% Change 1
23.702
12.807
0.21 2
27.092
14.329
2.37 3
30.466
16.434
0.38 4
33.374
17.987
0.46 5
36.294
19.546
0.54 6
38.72
20.832
0.64 7
41.195
22.139
0.75 8
43.137
23.182 9
45.603
24.478
0.87 10
48.063
25.77
0.98 11
49.054
26.291
1.02 12
51.064
27.33
1.17 13
53.04
28.362
1.26 14
55.04
29.398
1.37 15
56.55
30.17
1.49 16
58.6
31.213
1.65 17
60.19
31.986
1.89 18
61.8
32.769
2.11 19
62.97
33.277
2.46 20
64.87
34.061
3.12 21
67.03
34.577
4.96 22
68.18
34.427
7.23 23
70.33
34.474
10.46 24
72.85
34.332
14.89 25
75.62
33.3
22.96
Package #8 – Pin 21 – 400x

14. Summary
Simple thin film resistor networks have been fabricated with Titanium Carbide as a new material.
The excellent thermal and mechanical stability of TiC, together with TCR value make it a good candidate as an alternate thin film resistor material.
Pulsed Laser Deposition (PLD) was combined with Si- wafer processing techniques for fabrication of TiC resistor network.
Under pulsed power operation, TiC resistors remained intact, and testing was halted due to melting of Au wire bonds and metal interconnects.
TiC resistors were capable of withstanding up to 2 W of cw power.
Patent application submitted.

15. Potential Applications Future work
RF attenuators
Thin film hybrid circuitry
High power applications
Discrete resistors
Perform bias humidity testing

16. Acknowledgements Aerospace Corporation
Parts Materials and Process Department
Mrs. Katie Feistel
Dr. Wayne Martin
Scott Nuccio
Jeremy Young
Electronic Engineering Subdivison
Peter Carian
Laboratory Operations
Mrs. Barbara Hill