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Written by Jerod Mason, David Petzold, Aparna Joshi, Edward Aspell   
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Product Sensitivity Analysis on Multithrow TX/RX Switches

Jerod Mason, David Petzold, Aparna Joshi, Edward Aspell

 

Abstract

A method for data alignment of device characteristics as measured on Process Control Monitors (PCM) with the circuit level performance of adjacent multithrow switch circuits has been developed. This technique provides a powerful method for correlating extrinsic and intrinsic device characteristics with circuit performance. This method provides a valuable tool that is being used to improve device modeling, device development and production yields.

 

 

INTRODUCTION

The 2G/3G generations of communication systems including GSM/W-CDMA require components with the challenging combination of high linearity, low distortion, and low losses. A key component in this type of system is a multithrow TX/RX multithrow switch, which transmits high power from a front end module (FEM) in the TX mode and is switched to lower transmission power reception going to filters and linear power amplifiers (LNA) in the RX mode. In the transmit mode, the most important and challenging parameter is low harmonic generation under VSWR conditions. Typically for an input power level of 35 dBm and VSWR of 5:1 from the antenna, the harmonics generated should be below -30 dBm. The WCDMA mode input power is usually relatively low (28 dBm), but has a very challenging linearity requirement associated with the blocker performance and is expressed in Intermodulation distortion products (IMD) [1]. The dominant technology presently used for these multithrow TX/RX switches is GaAs pHEMT. This technology offers excellent power handling capability, but achieving the linearity performance and low harmonic generation remains challenging. One of the first steps needed to address this challenge is to increase the understanding of which extrinsic and intrinsic device characteristics can be correl ated to linearity and/or low harmonic generation of multi-throw switches. In this paper, a method for aligning and correlating extrinsic and intrinsic device characteristics that are measured on process control monitors with adjacent RF onwafer measured circuit performance is presented. The correlation of the 3rd harmonics of a single pole seven throw (SP7T) switch with extrinsic and intrinsic device characteristics measured on PCM’s will be used to demonstrate this powerful technique.

PROCESS CONTROL MONITOR TESTING

Process control monitor structures are included on all production wafers at Skyworks. The PCM structures are designed to be easily autoprobed, and to provide both extrinsic and intrinsic device level data. The extrinsic device characteristics that are measured on PCM’s include standard DC type parameters such as; saturated drain source current (Idss), maximum drain source current (Imax), pinch-off voltage (Vp), on-state resistance (Ron), transconductance (Gm), gate leakage currents (Ig), off-state drain leakage current (Ioff), device ideality (Nif), built-in voltage (Vbi) and breakdown voltages (Vb). The intrinsic data is measured at small signal and extracted using a proprietary methodology. These extracted intrinsic parameters include standard linear and saturated resistances, capacitances, and dispersion characteristics. RF ONWAFER CIRCUIT TESTING Extensive RF onwafer testing is performed on production pHEMT switch wafers. The circuit and I/O pad geometries are designed to be easily autoprobed. The test stand and probe cards are designed to minimize the effects of impedance on these measurements. Standard production onwaf er test includes measuring; insertion loss, leakage, isolation, 2nd harmonics, 3rd harmonics and intermodulation distortion.

PRODUCT SENSITIVITY ANALYSIS METHOD

A product sensitivity analysis (PSA) [2] was performed on a single pole, seven throw multi-mode TX/RX switch. The focus of the analysis was to gain insight into the device level characteristics that are involved with the generation of 3rd harmonics on this product. The PSA was performed on an engineering lot that was fabricated using a process that was slightly modified to provide wafers with varying intrinsic device characteristics. CS MANTECH Conference, April 14-17, 2008, Chicago, Illinois, USA

wafer map with PCM strcutures

Figure 1 Product Sensitivity Analysis Wafer Map

The product sensitivity analysis technique was used to align the autoprobed PCM data with immediately adjacent onwafer test data as depicted by the wafer map in Figure 1. The dark red colored devices in Figure 1 are PCM’s, while the lighter blue colored devices are circuits in a zone immediately surrounding each PCM. The mean and/or median value for the onwafer circuit test data from each zone were calculated then aligned to the PCM data from that site.

A sample of the results of PSA data alignment is shown in Table 1. This method provides a direct site specific alignment of PCM test data with onwafer circuit test data. The format of the resultant data set supports most available statistical analysis techniques.

Table 1. Product Sensitivity Analysis Data Alignment Sample

lot_id

wf_id

site

RFPCM

Idss-CS

RFPCM

Cg2

lack .5pt; padding: 0in 5.4pt 0in 5.4pt; height: 23.7pt;" width="92" valign="top">

RFPCM Vbgd3-Se3G

On-wafer

q2-Harm

On-wafer

q2-3Harm

3357553

13607422

320101

147.5

1077.5

29.0

88.8

82.5

3357553

13607422

450101

144.0

1070.2

29.0

89.9

82.1

3357553

13607422

540101

147.2

1090.9

29.1

88.2

80.9

3357553

13607423

230101

145.3

1161.8

29.1

87.4

80.8

3357553

13607423

350101

144.6

1169.7

28.9

88.3

81.2

3357553

13607423

450101

148.4

1143.4

28.5

88.2

80.5



 
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