Introduction
MEMS switches deliver exceptional benefits in bandwidth, isolation, leakage, and footprint compared to traditional electromechanical relays and solid-state switches. However, like all physical contact devices, MEMS switches are susceptible to failure mechanisms when operated under hot-switching conditions.
For MEMS switches, the dominant wear and failure drivers are:
- Voltage stress during turn-on: Off to On transition when voltage exists across the open contacts as the gap collapses.
- Current stress during turn-off: On to Off transition, when current continues to flow as contacts separate, often exacerbated by inductive or capacitive energy.
Hot Switching Events
Typically relay datasheets list separate specifications ratings for the Off to On and On to Off transitions. Often on datasheets these transitions are called “make” and “break” respectively. The Off to On transition refers to the relay closure process, where the contacts come into contact and close the switch path. Likewise, the On to Off transition refers to relay opening process, where the contacts begin to open and open the switch path. The Off to On and On to Off transitions have different associated failure mechanisms because of the physics of the contact system as the switch closes or opens. The description of the physical effects and the associated failure mechanisms follows.
On to Off Transition
On to Off Transition describes the physical effects of maintaining a load on the switch path and moving from On, or closed switch path state to the Off state or open switch path state. More directly, contacts are in a closed state and are opening with a load across the switch path. When opening a loaded contact path, the damage is mainly driven by current, specifically, an arc sustained by the current developed by the load. When the contacts begin to pull apart the current does not stop instantaneously. The resulting gap in the contacts creates an ionized air gap which forms an arc. The arc continues until the gap is large enough or the energy in the load is exhausted. In addition to the current, higher voltages cause the arc to persist longer giving the current more time to damage the contacts. In addition, if the load is inductive, the arc duration will be extended.
High current across the opening contacts causes the following failure mechanisms:
- Contact pitting
- Metal vaporization
- Material transfer between contacts
- Contact welding
Off to On Transition
Off to On Transition describes the physical effects of maintaining a load on the switch path and moving from Off, or open switch path state to the On state or closed switch path state. More directly, contacts are in an open state and closing opening with a load across the switch path. When closing a loaded contact path, the damage is mainly driven by voltage, specifically closing the gap enough to produce an arc. The severity of the damage cause the arc is dominated by current and the associate multiplication factor of the inrush current energy. As the contacts approach each other, the electric field increases across the decreasing contact gap. An arc may strike before the contact surfaces touch. After the contract surface touch, the current surges. So, the load voltage determines where and when the air gap ionizes. The nature of the load, specifically being capacitive, determines the inrush and surge current. As general result, breaking inductive loads causes the most damage followed by making a capacitive load.
High voltage across the closing contacts causes contact surface damage, while the high inrush and surge currents cause the following failure mechanisms:
- Contact welding
- Micro welding
- Surface melting
Why MEMS Is Different for Hot Switching
Hot switching stresses MEMS switches differently than traditional relays or solid-state switches due to the scale of the contact geometry and the electrical environment at the switching node.
Hot switching damage is concentrated at the contact: MEMS contacts separate and close over micron-scale gaps. Voltage during turn-on and current during turn-off are concentrated into very small physical areas, accelerating wear when switching under load.
Small parasitics define switching conditions: Because MEMS parasitic capacitance is extremely low, even small external capacitances can dominate the voltage and current seen at the contacts during switching. This directly affects arc initiation and duration.
Protection elements directly modify hot-switch conditions: Components added to reduce hot-switch stress change the electrical environment at the moment of switching. Added capacitance increases stored energy. Added leakage creates unintended current paths. Both influence contact stress.
Turn-on is driven by voltage, not steady-state current: During off to on transitions, the voltage across the open MEMS contacts at first touch determines arc initiation and contact heating. Techniques such as precharge and residual charge removal are therefore critical.
Turn-off is driven by current and stored energy: During on to off transitions, inductive and capacitive energy forces current to continue flowing as contacts separate. Current diversion, clamping, and sequencing directly control arc persistence.
Component placement matters as much as component choice: Protection components placed near the MEMS contact directly affect switching behavior. Placing protection at the load localizes energy and reduces stress at the MEMS contact.
Over-mitigation can reintroduce hot switching: If protection networks dominate the node, they can create new transient conditions that reintroduce voltage or current stress during switching events.
Methods to Reduce Hot Switching
There are many proven techniques to reduce hot-switching stress. Traditional relay protection techniques often mitigate these stresses by adding passive or active components. However, many of these techniques introduce additional capacitance, leakage, loss, and coupling paths that directly undermine the advantages that motivate MEMS adoption in the first place. 8 primary methods are defined here with the tradeoffs of each technique, along with design guidance to minimize parasitic impact and preserve the value proposition of MEMS switches. The 8 primary mitigation methods are split relative to On to Off state transitions and Off to On state transitions as described above.
On to Off Transitions
When mitigating On to Off transitions, the goal is to reduce the current stress. Ideally, this involves ensuring that the MEMS switch opens when current is near zero. Alternatively, the current can be diverted away from the switch contacts during the opening event. 4 methods for mitigating On to Off damage are shown in the table below and describe in detail in the section that follows.
Approach | Active Current Commutation or Diversion | Inductive Energy Clamping | RC or RCD Snubbers | Series Resistance and Current Limiting |
| Technique | Parallel semiconductor path turns on before MEMS opens, moving the current away from the MEMS | Clamp network at the load provides a controlled decay path for inductive current | RC or RCD network absorbs energy and limits dv dt across opening contacts | Series impedance limits peak current during MEMS opening |
| Benefit | MEMS opens at near zero current, minimizing arc energy and contact heating | Prevents voltage overshoot and sustained arcing during turn off | Reduces dv dt and peak voltage across the MEMS contact gap | Simple and effective reduction of peak current and arc energy |
| Challenge | Semiconductor capacitance and leakage can dominate MEMS parasitics and reduce isolation | Clamp capacitance and leakage often exceed MEMS parasitics by orders of magnitude | Snubber capacitance directly degrades isolation and bandwidth | Added impedance reduces signal integrity and increases loss |
| Design Guidance to Minimize Impact | Place commutation path at the load, use small devices, and control slew rate | Place clamps at the load, select for low capacitance, and isolate from MEMS node | Avoid snubbers across MEMS, minimize capacitance, or switch snubber only during transitions | Use resistance only in transient paths and keep values as small as possible |
Off to On Transition
When mitigating Off to On transitions, the goal is to reduce voltage stress. Ideally, this involves ensuring that the MEMS switch closes when voltage is near zero. Alternatively, the current should be reduced through the switch contacts during the closing event. 4 methods for mitigating Off to On damage are shown in the table below and describe in detail in the section that follows.
Approach | Precharge Architecture | Inrush Current Limiting at Closure | Residual Charge Removal | dv dt Control and Overvoltage Clamping |
Technique | Precharge path raises load voltage before MEMS closes | Series or active path limits inrush at first contact | Discharge path sets load node to known voltage | RC or clamp limits dv dt and peak voltage |
Benefit | Lowers voltage at first touch | Reduces inrush and contact heating | Eliminates residual voltage | Limits transient voltage stress |
Challenge | Added parasitics increase node capacitance | Added impedance reduces bandwidth | Bleed paths add leakage | Added capacitance degrades isolation |
Design Guidance | Place at load and disconnect after use | Use transient-only limiting | Use high-value or gated discharge | Keep off MEMS node and minimize C |
The challenge is to protect MEMS contact physics without letting the protection network redefine the electrical behavior of the system.
Discussion on Mitigating On to Off Transitions
This section provides additional description of the On to Off transition hot switch mitigation techniques.
Active Current Commutation or Diversion
Technique: A parallel solid-state path or controlled diversion route is enabled prior to opening the MEMS switch. Once current is commutated, the MEMS opens under near-zero current.
Consequence
- Adds semiconductor output capacitance that can dominate MEMS parasitics
- Introduces leakage and charge injection paths
- Can increase EMI due to fast dv dt switching
Design Guidance to Minimize Impact
- Place diversion elements at the load, not near the MEMS node
- Use minimum-geometry devices sized only for transient conduction
- Control gate slew to reduce displacement current
- Avoid connecting diversion paths to shared buses in matrix architectures
Inductive Energy Clamping
Technique: Flyback diodes, diode-Zener combinations, TVS devices, or active clamps are used to absorb inductive energy when opening under load.
Consequence
- Junction capacitance is often orders of magnitude larger than MEMS parasitics
- Leakage increases with temperature
- Slower current decay can affect system timing
Design Guidance to Minimize Impact
- Place clamps directly across the inductive load, not across the MEMS
- Select devices based on capacitance first, not just power rating
- Use small series impedance to decouple clamp capacitance from the MEMS node
- Prefer diode-Zener structures to reduce TVS size and capacitance
RC or RCD Snubbers
Technique: Snubbers reduce dv dt and absorb energy during contact separation.
Consequence
- Capacitors directly across the MEMS degrade bandwidth and isolation
- Creates AC coupling paths even when the MEMS is open
- Particularly harmful in RF, high-impedance, or matrix systems
Design Guidance to Minimize Impact
- Avoid snubbers across the MEMS whenever possible
- Place snubbers across the load or inductive element instead
- If unavoidable, minimize capacitance and compensate with higher resistance
- Consider switchable snubbers that are only connected during transitions
Series Resistance and Current Limiting
Technique: Small series resistors or transient current limiting elements reduce peak current during opening events.
Consequence
- Adds series loss, noise, and bandwidth reduction
- Introduces parasitic capacitance through resistor bodies and layout
Design Guidance to Minimize Impact
- Use resistance in transient or precharge paths, not the main conduction path
- Select resistor packages optimized for low parasitics
- Keep resistance values minimal and rely on sequencing where possible
Control and Sequencing
Technique: Cold Switching. The system disables stimulus, allows energy to decay, then opens the MEMS under cold conditions.
Consequence
- Increased control complexity
- Requires observability of node state
Design Guidance to Minimize Impact
- Prefer sequencing over added hardware whenever feasible
- If discharge paths are required, gate them so they are inactive during steady state
- Locate discharge networks at the load to preserve MEMS isolation
Discussion on Mitigating Off to On Transitions
This section provides additional description of the Off to On transition hot switch mitigation techniques.
Precharge Architectures
Technique: The load is precharged through a controlled path before the MEMS closes.
Consequence
- Adds leakage and capacitance on the switched node
- Can introduce unintended RC time constants
Design Guidance to Minimize Impact
- Implement precharge on the load side, not the MEMS side
- Prefer resistor-based precharge over MOSFETs
- If MOSFETs are used, select low-Coss devices and fully disconnect after precharge
- Avoid leaving precharge elements permanently in parallel with the MEMS
Zero-Voltage Switching and Controlled Ramps
Technique: MEMS closure occurs at voltage minima, or the source is ramped after closure.
Consequence
- Slower ramps may reduce system throughput
- Prolonged linear operation elsewhere can increase dissipation
Design Guidance to Minimize Impact
- Use event-based ramping, not continuous slow edges
- For AC systems, use phase-aware zero-voltage switching without slew reduction
- Prefer control-based solutions that add no analog parasitics
Inrush Current Limiting at Closure
Technique: Series resistors, NTCs, or active current limits reduce charging current into capacitive loads.
Consequence
- NTCs introduce temperature dependence
- Active limiters add capacitance, leakage, and noise
- Continuous limiters increase output impedance
Design Guidance to Minimize Impact
- Limit current only during the transient, then bypass
- Place active limiters upstream where impedance is already low
- Account for supply output capacitance, which can dominate inrush behavior
Residual Charge Removal
Technique: Bleed resistors or forced discharge steps ensure the load is at a known potential before closure.
Consequence
- Adds leakage and continuous power dissipation
- Can degrade isolation in high-impedance systems
Design Guidance to Minimize Impact
- Use the highest resistance consistent with discharge timing
- Gate bleed paths so they are inactive during steady state
- Place discharge networks on the load side of the MEMS
dv dt Control and Overvoltage Clamping
Technique: RC networks or TVS devices limit transient overvoltage during closure.
Consequence
- Directly increases node capacitance
- Can erase MEMS bandwidth and isolation benefits
Design Guidance to Minimize Impact
- Keep all capacitance off the MEMS side
- Select explicitly low-capacitance protection devices
- Use control-based techniques first, passive components last
Design Principles for Preserving MEMS Value
- Prefer control and sequencing over hardware These add negligible parasitics and are the most MEMS-friendly solutions.
- Localize protection at the load Keep capacitance, clamps, and energy absorption away from the MEMS node.
- Avoid capacitors across MEMS contacts This directly negates isolation and bandwidth benefits.
- Use transient-only protection paths Disconnect protection elements during steady-state operation.
- Treat parasitics as first-order design constraints In MEMS systems, parasitic capacitance and leakage define system performance.
Cenfire’s Perspective
Cenfire MEMS switches are designed to enable system-level solutions that reduce hot-switching stress without relying on parasitic-heavy protection networks. By combining robust MEMS device physics with disciplined system architecture, designers can achieve both long-term reliability and uncompromised signal integrity.