LDMOS degradation issue

hassanferoze073 — Fri, 30 Nov 2018 07:11:18 GMT

I want to ask a query regarding the performance of NXP LDMOS Power Transistor part No. mmrf1312H. I am facing the reliability issue of the said device. I successfully achieved the desired parameters from the device which are stated below as:

RF Output Power Level (peak) = 60dBm (1000W)
Efficiency= 55%
Gain = 16.5 dB

Operating parameters are given below:

VDD=50V
(supply was providing +30V, DC-DC converter was used to get +50V)
Quiescent current =100mA (VGS=1.94V)
Pulse Width = 256usec
PRF=400Hz
Duty Cycle= 10%
Operating Temperature = 25 degree centigrade

After successfully achieved the desired parameters, i turned the device on for longer span to check the reliability of the device, but after 40 minutes suddenly the device output power drops to 200W, i turned off the power supply and did check the device via DMM. The gate terminal of the device showed short circuit.

Again i performed the test by installing the new device into the circuit. it successfully produced an output power of around 1000W but after 70 mins, it got damaged too.

I tested 8 devices, all of them got damaged gradually. Some devices were moderately failed and some were completely failed. Their life time span was 40mins, 70mins, 200mins, 30mins, 50mins, 120mins, 80mins, 20mins respectively.

Please note that the following mentioned precautions were taken while performing the test.

RF Input Power level was under 20W as provided in the datasheet.
Isolator was inserted at the output line of transistor to protect the device from high VSWR.
Heat sink temperature was continuously monitored, it was around 45 degree at the time when device got damaged.

I am so confused, what could be the reason, please help me, i shall be very thankful to you

Re: LDMOS degradation issue

LPP — Mon, 03 Dec 2018 10:53:56 GMT

The gradual device degradation can be a consequence of repeated avalanche condition caused by the drain over-voltage.

Typical reasons of over-voltage is high VSWR or transient spikes.

In the case of RF pulse signal, the over-voltage can be caused by RF envelope oscillation at the RF pulse edges because of low frequency resonance of RF choke inductance and output capacitance of the transistor.

Typical recommendation is to decrease slew rate of input signal RF envelope

Have a great day,
Pavel

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

topic LDMOS degradation issue in Other NXP Products

LDMOS degradation issue

Re: LDMOS degradation issue