A NEW DC MEASUREMENT PRINCIPLE TO FULLY COVER DEVICE SELF-HEATING

Transcription

1 -1- A NEW DC MEASUREMENT PRINCIPLE TO FULLY COVER DEVICE SELF-HEATING Keywords: Device Self-Heating During DC Measurement, Data Sampling After Self-Heating Reached Final Value, IC-CAP Demo File Contents: A New DC Measurement Principle to Fully Cover Device Self-Heating... 2 The new Measurement Principle Step-by-Step... 6

2 -2- A New DC Measurement Principle to Fully Cover Device SelfHeating id [ma] A New DC Measurement Principle To Fully Cover Device Self-Heating (C) Franz Sischka, March 2015 vds [V] This paper introduces a new measurement principle for power devices, ensuring measurements to be taken at the final, steady-state device over-temperature of each measurement step.

3 -3- Evaluating the Self-Heating Effect of a Packaged MOS Transistor SMU2 Measurement of MAX(vDS) vs. time for different vgs values id(time) vgs 2.5 V, 2.7V, 2.8V, 2.9V + - 2N7000 id [ma] SMU1 vds=10v id current drifts due to self-heating, when vgs and MAX(vDS) are applied infinitely vds=10v 2 When biased by a constant vds (10V), and a constant vgs (2.5V, 2.7V, 2.8V, 2.9V), the measured Drain current id will drift to higher values, due to the increasing self-heating of the MOS transistor, as sketched by the colored arrows above. Note: the black measurement curve is a default DC Analyzer measurement result. As will be shown later, it does not represent the real steady-state device performance when self-heating of the device happens: The end points of the id-vds traces of a steady-state over temperature measurement result should end up at the ends of the colored arrows.

4 -4- Self-Heating over Fixed Bias vgs = 2.9V vgs = 2.9V vgs = 2.8V vgs = 2.8V vgs = 2.7V vgs = 2.7V vgs = 2.5V vgs = 2.5V Measurement Setup The self-heating, i.e. the increase of id, can take hundreds of seconds! -3- The slide above depicts the drift of the Drain current vs. time, due to the self-heating. On a linear time axis, it is represented by an exponential function, as expected. The same Drain current drift, however, displayed with a logarithmic time axis makes it obvious that changing the measurement 'Delay Time' of a Semiconductor Analyzer from its default milli-seconds (SHORT Integration Time) to usually hundreds of milli-seconds (LONG Integration Time) does not really help. Depending on the power dissipation of the bias point, much longer delay times can be required. Difference between a 'quick' measurement and the real, steady-state self-heated measurement DC Output Characteristics conventional thermal drift vgs = 2.9V [ma] vgs = 2.8V correct id vgs = 2.7V vgs = 2.5V vds [V] Standard measurement: Integr.Time: S Hold Time: 0 sec Delay Time: 0 sec time [LOG] [sec] Waiting at every bias point until the final self-heating is reached vds [V] The *real*, steady-state self-heated measurement result 4

5 -5- Only when the Drain current is measured *after* the device has reached its corresponding final overtemperature, the *real* DC output characteristic can be obtained. This will lead to extremely slow measurement results. Therefore, a new measurement procedure is suggested, as explained by the next slides. The Basic Idea of the New High-Power Device Measurement Procedure: The Power-Dissipation-Related Measurement Stepping blue: equal power dissipation traces The new measurement principle begins with a conventional id-vds pre-measurement. In a second step, the power dissipation at every bias point is calculated, and the results are ordered with increasing power. Finally, the final measurement is performed by stepping down the ordered power dissipation index sequence (see the arrows) This avoids the several up and down heatings during conventional sweep stepping. 5 Back to Top

6 -6- The new Measurement Principle Step-by-Step The new Measurement Principle Step-by-Step... 6 Proposing a New, Consistent Self-Heating-Covering Measurement Principle: id_premeasured.m id.m perform a conventional Pre-Measurement with Power-Consumption-Dependent Hold Times i.e. 1st sweep is a vd up-ramping, and the 2nd sweep is a vg up-ramping at the max. Power Biasing, keep the biasing ON, and wait until the measured current has stabilized perform the Power-Consumption-Based Down-Ramping (see the next slides) 7

7 -7Begin of the new proposed measurement procedure: Proposing a New Full Self-heating Measurement Principle id_premeasured.m id.m performing the power-consumption-based down-ramping... (cont'd): 8 The new proposed measurement procedure half-way done: Proposing a New Full Self-heating Measurement Principle (cont'd): id_premeasured.m id.m performing the power-consumption-based down-ramping... 9

8 -8- Proposing a New Full Self-heating Measurement Principle (cont'd): id_premeasured.m id.m The Final Measurement Result 10 The slide above depicts the final measurement result (red), taken at every bias point at the final, steady-state over-temperature, compared to the pre-measurement. measured accurate, fully self-heated current id [ma] Visualization of The Implemented Measurement Stepping measurement result visualized stepping sequence of measured points, beginning with the highest power dissipation, down to lowest. vds [V] -11- The blue traces represent the obtained, correct thermal steady-state id-vds measurement result, while the red traces visualize the measurement stepping, from highest power dissipation down to the lowest.

9 -9- (cont'd) The same in LOG/LOG Scale... Dissipation Power [LOG] [Watt] Visualized Measurement Steps vds [LOG] [V] -12- Note: Demo available for IC-CAP Users For users of IC-CAP, a ModelFile is available applying anhp4142 DC Analyzer. The demo can easily be converted for HP/Agilent/Keysight 415x, E527x and B1500 Infos: contact@sisconsult.de Back to Top contact@sisconsult.de -14-