Neil Hao

Starts from 2021/Oct/21 to 2023/02/11 17:30 (Last Modification)

My friend's company has capability to manufacture high precision circuit based on photolithography process. At current process node, the minimum trace width is 5um and the substrates can be either HTCC (High Temperature Co-fired Ceramic) or LTCC (Low Temperature Co-fired Ceramic). We are digging in the possible RF applications for current process node. Thus, the dielectric constant is one of the important characteristics which has to be measured.

There are serval methods for dielectric constant measurement. A very specific test method which may or may not correlate to the microwave application of interest. The Dielectric Constant which is reported for a material can be dramatically different by the test methods. [1] In this article, a HTCC substrate is measured by using the Ring Resonator method.

The Ring Resonator method has following advantages [2]:

1. A closed ring with no gaps eliminates much of the fringe effect.
2. Resonator rings ensure minimal or negligible loss by radiation, so that Er can be calculated more accurately.
3. The results refer to very narrow band ranges/widths (resonance); this avoids issues connected to spurious modes.

The substrate thickness is 0.5mm and silver conductor thickness is 5um. HTCC substrate was manufactured by using Al2O3 thus the Er could be expected to be about 9.8.

According to above data, the width of 50 Ohm microstrip line is 0.48mm. Finally, the resonator ring could be designed with a 20mm radius ring, 0.4mm gap and 0.48mm microstrip line width.

The ring will resonate at multiples of lambda which corresponding to the circumference of the ring.

For example, Fo(n) = n*(C0/l) when Er =1. C0 = 2.99792458×108m/s l = 3.14*40mm = 0.12566m

Thus,