Background
In Radio Frequency (RF) on-chip inductance model extraction, it is necessary to test the S-parameters of the device at different frequencies. A special inductance test structure, PAD (PAD) and wire (Feed line) connecting PAD and inductance, is required to make the measurement feasible. Due to their parasitic effects, they all have a certain effect on the accuracy of the inductance measurement. Therefore, when measuring inductance, one critical issue is how to remove the parasitic effect of the inductance test structure. For the case of low frequency, the parasitic effect of the lead can be ignored, so the measured value can be achieved by removing the parasitic effect of the bonding pad. At this time, the used inductance test structure of the PAD is called an open structure (open structure), namely, a hollow structure (dummy structure) only having the PAD but not having the inductance is needed, most of the current inductance measurement on the radio frequency chip focuses on only using the open structure (open structure) to remove the parasitic effect of the PAD, and the method can basically remove the parallel parasitic capacitance of the PAD structure and the like, is simple and convenient, and is suitable for the application of lower frequency. However, as the frequency increases, the parasitic effect of the lead wire also has a larger influence, so that the limitation of the inductance testing method of the OPEN structure is also shown.
Disclosure of Invention
The invention aims to solve the technical problem of providing a radio frequency on-chip inductance measuring method capable of removing parasitic effects on a test structure, which can simultaneously remove the parasitic effects generated by a bonding pad and a lead in an inductance test structure when the radio frequency on-chip inductance is measured, thereby realizing the purpose of accurately measuring the on-chip inductance of the radio frequency.
In order to solve the technical problem, the method comprises the following steps:
(1) introducing a path structure, namely connecting a connecting wire with the same width as a lead wire of the test inductor between two bonding pads connected with signals;
(2) calculating S parameter test value after the passage structure is opened to remove parasitic effect, and converting the S parameter into corresponding ABCD parameter A_deembopen;
(3) Calculating characteristic impedance Z and a transmission constant gamma by using the S parameter obtained in the step (2);
(4) respectively calculating the ABCD parameters A of the left lead and the right lead in the test structure based on the characteristic parameters Z and gamma obtained in the step (3)_leftAnd A_right;
(5) ABCD parameter A based on the left and right leads_leftAnd A_rightCalculating the ABCD parameter A of the inductance measurement on the radio frequency chip after the parasitic effect of the lead is removed_dut;
(6) The ABCD parameter A of the inductance measurement on the radio frequency chip after the parasitic effect of the lead is removed is obtained through calculation_dutConverted into the corresponding S parameter.
By adopting the technical scheme, the invention has the following beneficial effects that on the basis of removing the parasitic effect brought by the PAD in an open-circuit structure measurement mode on the inductance measurement value, the parasitic effect brought by the lead wire is removed from the inductance measurement value by using a through structure measurement mode, so that the accurate inductance measurement value can be obtained.
Detailed Description
Referring to the attached drawings, the test structure of the invention is shown in a test schematic diagram, and the method of the invention comprises the following steps:
(1) a new hollow structure-channel structure is introduced, namely a connecting wire with the same width as the lead wire of the test inductor is connected between two PADs connected with signals.
(2) Calculating an S parameter test value of the path structure (through structure) after an Open-circuit structure is used for removing the parasitic effect (Open De-embedding) of PAD, and converting the S parameter into a corresponding ABCD parameter A_deembopen。
The step is mainly used for removing the parasitic effect of the PAD, which is mainly expressed as parasitic capacitance, and the method for calculating the S parameter test value after the parasitic capacitance is removed comprises the following steps:
a. after the measurement structure is calibrated, the S parameter of the inductor on the radio frequency chip is directly measured and converted into the corresponding Y parameter Y_measAs is well known to those skilled in the art, the measured on-chip S parameter measurements include both PAD parasitics and wire parasitics;
b. measuring S parameter of PAD in open structure (open structure), converting it into corresponding Y parameter_PADThen using Y obtained in step a_measMinus the Y_PADObtaining the corresponding Y parameter of the inductor after the parasitic effect of the PAD is removed, wherein the calculation formula is as follows:
Y_deembopen=Y_meas-Y_PAD
c. calculating the obtained Y parameter Y_deembopenAnd then converted into its corresponding S parameter.
(3) And (3) calculating the characteristic impedance Z and the transmission constant gamma by using the S parameter measured in the step (2).
Wherein, the calculation formula of the transmission constant gamma is as follows:
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wherein,
the calculation formula of the characteristic impedance Z is as follows:
(4) respectively calculating the ABCD parameters A of the left and right leads with different lengths in the test structure based on the characteristic parameters Z and gamma obtained in the step (3)_leftAnd A_rightWherein A is_leftRefers to the ABCD parameter, A, of the left lead in the test structure_rightRefers to the ABCD parameter of the right lead in the test structure.
The calculation formula of the ABCD parameter is as follows:
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wherein L is the length of the lead wire
(5) Since the inductor is cascaded with the two leads, the ABCD parameter A of the left and right leads can be based_leftAnd A_rightCalculating the ABCD parameter A of the inductance measurement on the radio frequency chip after the parasitic effect of the lead is removed_dut。
The calculation formula is as follows:
A_dut=(A_left)-1*A_deembopen*(A_right)-1
(6) the ABCD parameter A of the inductance measurement on the radio frequency chip after the parasitic effect of the lead is removed is obtained through calculation_dutConverted into the corresponding S parameter.
The accurate measurement value of the intrinsic inductance on the radio frequency chip can be measured through the process.