Power durability measurement of radio frequency surface acoustic wave and bulk acoustic wave devices taking the influence of their temperature dependences into account

Abstract

In this paper, we describe the study of time to failure (TTF) evaluation of radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices for the International Electrotechnical Commission (IEC) standardization. As the passband shifts with T due to the nonzero temperature coefficient of frequency (TCF), its influence must be taken into account at the acceleration test. A technique to estimate the frequency-dependent TCF of RF SAW/BAW devices for the acceleration test of the TTF estimation is proposed. First, it is shown how the filter passband shifts with T, and its numerical model is proposed. Then, its impact on the power durability test is presented. © 2018 The Japan Society of Applied Physics High power durability is demanded from radio frequency (RF) surface and bulk acoustic wave (SAW=BAW) devices, which are widely used in current telecommunication systems. [1][2][3][4][5][6][7][8][9][10][11] Power durability is evaluated on the basis of time to failure (TTF), and depends on not only the applied power P and the chip temperature T but also the driving frequency f. At TTF measurement, excess P and T are applied to the device under test (DUT) to shorten TTF to a realistic value, and TTF is estimated from a numerical model established from a series of measurement data. However, the acceleration test procedures have not been standardized for RF SAW=BAW devices yet.It is known that the passband shifts with T owing to the nonzero temperature coefficient of frequency (TCF). It means that the weakest frequency point in terms of TTF changes with T, and thus its effect must be taken into account in the acceleration test.The authors are currently investigating the test procedure so as to establish an international standard as the International Electrotechnical Commission (IEC) activity in collaboration with SAW industries all over the world. For example, the authors proposed the use of bulk wave responses to estimate chip temperature in packaged SAW devices.12) Such estimation is necessary because the TTF is determined by the chip temperature instead of the environmental one.In this paper, we propose a technique of estimating the frequency-dependent TCF of RF SAW=BAW devices for the acceleration test of the TTF estimation. First, it is shown how the filter passband shifts with T, and its numerical model is proposed. Then its impact on the power durability test is presented. Figure 1 shows the measured insertion loss of a ladder SAW filter for WCDMA Band 1 Tx (frequency range: 1,920-1,980 MHz) on 42°YX-LiTaO 3 (42-LT) 13) for a few T settings. The filter passband shifts to the low-frequency side with T. It is also seen that the TCF is slightly larger at the upper passband edge than at the lower passband edge. This means that the TCF has frequency dependence.This passband translation is modeled as follows. First, the filter response is measured at various T values. Hereafter, we denote the measured transfer function at the frequency point f n and the temperature T = ΔT + 20°C as H ΔT ( f n ). Then,2 þ a 3 ÁT 3 Þ,...