System and method for detecting surface charges of a MEMS device
AssigneeAnalog Devices, Inc.
InventorsFang Liu, Kuang L. Yang
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Abstract
A method for measuring retained surface charges within a MEMS device includes performing an initial voltage sweep on the MEMS device, and recording the capacitance between a first and second electrode of the MEMS device. The method may then (1) apply a stress signal to the MEMS device that causes a first and/or second electrode within the MEMS device to retain a surface charge, and (2) perform at least one additional voltage sweep on the MEMS device. The method may record the capacitance during the additional voltage sweep(s), and calculate a C-V center voltage shift based upon the data obtained during the initial voltage sweep and additional voltage sweep. The voltage shift is representative of the retained surface charge.
Claims27
A method for measuring a retained surface charge within a MEMS device comprising:
- (i) performing an initial voltage signal sweep on the MEMS device, the MEMS device including a first and second electrode;
- the initial voltage signal
- sweep including applying a first force voltage signal to a substrate and the second electrode of the MEMS device and gradually changing the applied first force voltage signal, which changes a capacitance between the first and second electrode;
- (ii) applying a stress voltage signal to the MEMS device for a pre-determined amount of time, the stress voltage signal causing at least one of the first and second electrodes to retain a surface charge;
- (iii) performing an at least one additional voltage signal sweep on the MEMS device after applying the stress voltage signal, the at least one additional voltage signal sweep including applying a second force voltage signal to the MEMS device and gradually changing the applied second force voltage signal, changing the second force voltage signal which changes the capacitance between the first and second electrode;
- (iv) calculating a signal shift based upon data obtained in (i) and (iii), the signal shift being representative of the retained surface charge.
A method for characterizing surface charges within a MEMS device having a first and second electrode, the method comprising:
- (i) applying a force voltage signal to a substrate and the second electrode of the MEMS device, the force voltage signal creating a capacitance between the first and second electrode;
- (ii) gradually changing the applied force voltage signal to change the capacitance between the first and second electrodes;
- (iii) applying a stress voltage signal to the MEMS device for a pre-determined amount of time, the force voltage signal causing at least one of the first and second electrodes to retain a surface charge;
- (v) repeating (i) through (iii) for a pre-determined number of times;
- (vi) calculating a signal shift based upon data obtained in (ii), the signal shift being representative of the retained surface charge.
A test system comprising:
- a MEMS capacitor having a first electrode and a second electrode, the first and second electrode being separated by an air gap;
- a signal generator configured to perform at least one signal voltage sweep and apply a stress voltage signal to the MEMS capacitor, the signal sweep including applying and gradually changing a force voltage signal to the MEMS capacitor thereby changing a capacitance between the first and second electrode, the stress signal causing at least one of the first and second electrodes to retain a surface charge, the signal generator applying the stress signal to the MEMS device for a pre-determined amount of time;
- a signal monitor configured to measure the capacitance between the first and second electrode as the applied force voltage signal is increased, the signal monitor configured to communicate with a data analysis device configured to calculate a signal shift based, at least in part, upon the applied force signal and the capacitance measured by the signal monitor, the signal shift being representative of the retained surface charge.
Dependencies are inferred from the claim text.