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PROC. 29th INTERNATIONAL CONFERENCE ON MICROELECTRONICS (MIEL 2014), BELGRADE, SERBIA, 12-14 MAY, 2014

Investigation of Dose Rate and TID Effects in Anisotropic Magneto Resistive Sensor

A. V. Grebenkina, D. V. Boychenko, A. Y. Nikiforov,

V. A. Telets, V. V. Amelichev, V. A. Kharitonov

Abstract— Results of anisotropic magneto-resistive (AMR)

sensor dose rate and total dose behavior are presented. Experiments conducted at LINAC and pulsed electron accelerator. A good agreement of theoretical and experimental transfer functions was found. Investigated AMR-sensor radiation behavior can affect device operation in space applications.

I. INTRODUCTION

Though anisotropic magneto-resistive (AMR) effect is well known for a long time, a mass production of sensors on its basis has mastered just in last decade [1-3]. Such sensors are expected to possess high sensitivity, high-speed performance and noise immunity. Sensitive elements of such sensors, as a rule, are made of thin ferromagnetic layers. Only one magnetic domain can fit in such layer (Fig. 1).

Fig. 1. Domain structure of the degaussed thin magnetic film.

So, the resulting magnetic state of the sample is defined as the external field applied to the sample H, and the internal field of molecular currents, which is characterized by magnetization J - intensity created by electron shell microcurrents: B=μo(H+J). An external magnetic field H rotates the magnetization vector J of the film by an angle β. The value of β depends on direction and magnitude of the external field.

In general, the vectors H and J do not have the same direction. In the thin film element they can be considered arbitrarily oriented with respect to the axes of easy and hard magnetization, but always located in the plane of the film.

In order to increase linearity, some sensors are built with layer cake structure where ferromagnetic alloy (permalloy) alternate with metal. (Fig. 2.)

Fig. 2. AMP-element layer cake structure. Resistance due to magnetic field for such structure

where the angle β is 45° can be expressed as:

where R - AMP element resistance, RB=0 - resistance at

zero magnetic field, Rmax - maximum change in resistance due to magnetic field, H - measured magnetic field, H0 - magnetic bias field.

Anisotropic magnetoresistive transducers, in particular, and resistive transducers in general are one of the most common used devices in the chips as transducers. The most obvious method of measuring resistance, a method comprising passing a direct current through the resistor element and then measuring the voltage drop. Wheatstone bridge circuits are convenient for such voltage change control (Fig. 3).

Fig. 3. Wheatstone bridge AMR sensor.

Power dissipated in the resistive sensor must be small enough to avoid errors associated with self-heating of the sensor. Therefore, the nominal drive current should be minimized.

Alexandra V. Grebenkina, Dmitry V. Boychenko, Alexander Y. Nikiforov, Vitaly A. Telets are with National Research Nuclear University (NRNU) “MEPHI”, Moscow, Russian Federation (e-mail: avgreb@spels.ru).

Vladimir V. Amelichev is with Scientific-manufacturing complex "Technological Centre" MIET, Moscow, Russian Federation.

Vadim A. Kharitonov is with Rosatom Corporation, Russian Federation.

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For this reason, AMR sensors are made of a four equal magnetoresistors formed by depositing a thin layer of permalloy on a silicon wafer in the form of a square connected to the Wheatstone bridge circuit shoulders.

Such bridge is in zero (balanced) state when the equality R1/R4=R2/R3 takes place regardless of resistance magnitude, output signal (current or voltage) or measurement circuit.

II. EXPERIMENTAL RESULTS AND DISCUSSION

We chose one of the AMR sensors in order to experimentally evaluate its total dose and dose rate sensitivity and compare it with other sensors and peripheral circuitry for space applications [4-16].

Investigated device under test PMP-AMR-NH (Scientific-manufacturing complex "Technological Centre" MIET) parameters are shown in Table 1. Table 1. PMP-AMR-NH sensor parameters.

Parameter, unit Parameter Designation

Standard min max

Resistance, Ω Rm 1,5 2,5 Magnetic field sensitivity, mV S 2,5 -

Magnetic field range, mT B -0.1 0.1 Linearity,% NL - 5

The primary preparation goal was to achieve the

dependable measurement of the DUT transfer function on regular basis. Theoretical and experimental linear transfer functions for magnetic field range from -0.1 mT to 0.1 mT are shown in Fig. 4 and 5.

Fig. 4. AMR sensor resistance vs magnetic induction theoretical transfer function. The magnetic field was created by an electromagnet and measured automatically. The relative magnetic field sensitivity S was evaluated as S = V0/(Vin*Н).

This sensitivity is achieved in PMP-AMR-NH sensor by implementation of the Wheatstone bridge with four magnetoresistors in each shoulder.

H, mT-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15

-20

0

20

40sample 1 sample 2sample 3 sample 4 sample 5sample 6 sample 7 sample 9

V 0, m

V

Fig. 5. AMR sensor experimental transfer functions.

Dose rate responses of the sensor’s bridge and its each

shoulder at different dose rates were acquired at pulse linear electron accelerator ARSA (SPELS) and are shown in Fig 6. Rather significant bridge response was observed at relatively low dose rate level which is due to non-identical dose rate behavior of the bridge shoulders.

T

T

T

a) 500mV/del., 50ns/del.

T

T

T

b) 2 V / div., 50ns/del.

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TT

T

c) 5 V / div., 5 ms / div. Fig. 6. AMR sensor voltage output dose rate response a) 3,0•107 rad(Si)/s; b) 3,0•109 rad(Si)/s; c) 1,5•1010rad(Si)/s.

Total dose irradiation was conducted at LINAC

"RELUS" (SPELS), operating in X-ray mode. Its average energy is 800 keV and the maximum energy is 4.1 MeV. Sensors under test performed both zero output shift and sensitivity decrease during γ- irradiation (Fig. 7). The above observed behavior can be due to the formation in the structure of a radiation-induced charge, with a field oppositely directed to the total field vector in each domain [17].

Н, mT-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15

V 0, m

V

-30

-20

-10

0

10

20

D=0D=3.6e5D=6e5D=9e5D=1.2e6

Fig. 7. PMP-AMR-NH sensor’s transfer function TID behavior.

III. CONCLUSION AMR sensors are proved to be dose rate and TID

sensitive at the same levels as peripheral circuitry. That should be taken into account because could affect the instrumentation functionality in space applications.

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