Resonant Switch Charge Pump Eliminates Diode Voltage Drop
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Solution Overview
Problem
Conventional microelectromechanical systems (MEMS) switches have low closure cycle lifetimes and limitations in generating high voltages, which restrict their applications, especially in MEMS devices that require higher voltages for optimal performance.
Innovation Solution
The use of micromechanical resonant switches (resoswitches) in a Dickson charge pump configuration, which employs gated-sinusoid excitation and resonance operation to boost input voltages without diode voltage drops, allowing for higher output voltages and extended cycle lifetimes, and utilizes materials like ruthenium and nickel to reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MEMS switches are used, then device simplicity is maintained, but cycle lifetime is low and voltage generation is limited
Solution Approach 1:
The patent employs resonant mechanical vibration of the MEMS switch at its natural frequency to achieve high-cycle lifetime operation. The resonant oscillation allows the switch to operate for extremely high cycle counts (173.9×10^12 cycles) by minimizing mechanical stress and wear through smooth, periodic motion at the resonant frequency, thereby resolving the contradiction between reliability and device simplicity.
Solution Approach 2:
The patent changes the operational parameters by using gated-sinusoid excitation instead of conventional switching signals. This parameter change allows the switch to operate in resonance mode, achieving both high reliability and maintaining relative device simplicity. The sinusoidal gating function modulates the drive signal to synchronize with the resonant frequency, enabling the switch to achieve extended cycle lifetime without significant increase in device complexity.
2Power
If conventional CMOS charge pumps are used, then fabrication process is simple, but output voltage is limited by diode voltage drops and breakdown voltage
Solution Approach 1:
The patent replaces the electrical diode-based voltage multiplication mechanism with a mechanically resonant switch-based charge pump. The resonant MEMS switches mechanically open and close to transfer charge between capacitors, eliminating the need for diode voltage drops and breakdown voltage limitations. This substitution allows output voltages to exceed conventional CMOS limits while maintaining compatibility with standard CMOS fabrication processes, thus resolving the contradiction between power output and ease of manufacture.
3Reliability
If resonant switches are used with gated-sinusoid excitation, then cycle lifetime and output voltage are improved, but drive voltage requirements increase
Solution Approach 1:
The patent employs periodic gated-sinusoid excitation that is synchronized with the resonant frequency of the switch. This periodic action at the natural resonant frequency allows the system to build up oscillation amplitude efficiently, reducing the required drive voltage compared to non-resonant operation. The periodic gating function turns the resonant switch on and off at optimal moments in the oscillation cycle, maximizing energy transfer and minimizing the voltage required to achieve and maintain resonance, thereby resolving the contradiction between reliability improvement and drive voltage requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resonant switch-based charge pump achieves significantly higher cycle lifetimes and output voltages, eliminating the need for custom high-voltage CMOS technologies and enabling the use of a wider range of input voltages, thus enhancing MEMS device performance and reducing fabrication costs.
Implementation Method 1
The resonant switch includes an electrostatically-driven shuttle that is driven into oscillation by an AC voltage applied to a drive electrode
Implementation Method 2
When a sufficient amplitude of oscillation is achieved, then the shuttle contact impacts the output electrode, thereby activating the resonant switch
Data Source
AI summary
A circuit of N micromechanical resonant switches (resoswitches) is presented, which mimics a Dickson charge pump to amplify an input voltage to an output voltage of N plus 1 times the input voltage, while avoiding the diode voltage drop and breakdown voltage limitations of CMOS-based conventional charge pumps. Important aspects of successful charge pumping are: 1) the long cycle lifetime of resonant micromechanical switches, which has been shown to operate 173.9×1012 cycles, is orders of magnitude higher than non-resonant switches; 2) the use of gated-sinusoid drive excitation to allow a charging period independent of resoswitch resonance frequency; and 3) the use of resonance operation to lower required drive and DC-bias voltages to below the supply voltage. This mechanical charge pump obviates the need for custom high voltage CMOS for applications where large voltages are needed such as MEMS-based timing references, thereby allowing the use of virtually any CMOS process.