IoT Applications Moshe Avraham 1 , Gady Golan 1 , Michele Vaiana 2 , - - PowerPoint PPT Presentation

Wafer Level Packaged CMOS-SOI-MEMS Thermal Sensor at Wide Pressure Range for IoT Applications

Moshe Avraham1, Gady Golan1, Michele Vaiana2, Giuseppe Bruno2, Maria Eloisa Castagna2, Sara Stolyarova3, Tanya Blank3, Yael Nemirovsky3,4

1

• 1. Ariel University, Ariel, 40700, Israel
• 2. STMicroelectronics, Stradale Primosole, 50 – 95121 Catania, Italy
• 3. Electrical Engineering Dept., Technion- Israel Institute of Technology, Haifa 32000, Israel
• 4. TODOS TECHNOLOGIES Ltd., Israel.

Presented at the 7th Electronic Conference on Sensors and Applications, 15－30 November 2020; Available online: https://ecsa-7.sciforum.net/.

RESEARCH MOTIVATION

2

▪

IR sensors have huge markets: IoT, Smart homes, Automotive, etc

▪

Thermal sensors detect temperature changes induced by remote sensing of IR radiation and provide uncooled IR sensors

▪

MEMS enable high performance miniature thermal sensors

From: https://www.todos-technologies.com/

RESEARCH INNOVATION: TMOS

3

▪ The TMOS (Thermal-MOS) is a thermal sensor developed at the Technion ▪ Achieved by CMOS-SOI-MEMS process ▪ CMOS transistor is the standard building block of CMOS CHIPS manufactured in FABs ▪ By applying backend machining – TMOS becomes the highest performance thermal

sensor (compared to bolometers, PYRO’s and thermopiles)

▪ Operation at subthreshold requires very low power

Suspended Transistor Holding arm Micro-machined cavity Silicon bulk Buried

• xide

Oxides

Schematic cross-section of the TMOS layers 3D TMOS pixel Schematic Fabricated TMOS sensor

TMOS OPERATION PRINCIPLE

4

The micro-machined thermally insulated transistor has very low thermal mass and very low thermal conductivity Absorbed photons increase the TMOS temperature and modify the current-voltage characteristics Transistor voltage detects temperature changes at subthreshold

Suspended Transistor Holding arm Micro-machined cavity Silicon bulk Buried

• xide

Oxides

IR radiation t Δ𝑈

WAFER LEVEL PROCESSING AND VACUUM PACKAGING

5

▪

Currently on 8-inch wafers and 0.13𝝂𝒏 CMOS-SOI PROCESS

▪

3 silicon wafers are bonded

▪

vacuum of 10¯⁵ atm

▪

stable over 5 years

Bottom silicon wafer MEMS and TMOS wafer Top silicon optical window wafer

THE RESEARCH QUESTION

6

▪ Residual pressure determines the thermal conductance - 𝑯𝒖𝒊 ▪ thermal time constant 𝝊𝒖𝒊 =

𝑫𝒖𝒊 𝑯𝒖𝒊

▪ What is the effect of the residual vacuum upon performance? ▪ What pressure is critical for the proper performance of the device?

t

𝜐𝑢ℎ

Δ𝑈

∆𝑈

𝑡𝑡

THERMAL MODELING OF THE PACKAGED TMOS SENSOR

7

▪

The power balance equation: 𝜃𝑄

𝑝𝑞𝑢 = 𝐷𝑢ℎ 𝑒

Τ ∆𝑈 𝑢 𝑒 𝑢 + 𝐻𝑢ℎ∆𝑈(𝑢)

▪

In steady-state: ∆𝑈

𝑡𝑡 = 𝜃𝑄𝑝𝑞𝑢 𝐻𝑢ℎ

▪

The thermal conductance is determined by three mechanisms: 𝐻𝑢ℎ = 𝐻𝑡𝑝𝑚𝑗𝑒𝑡 + 𝐻𝑕𝑏𝑡 + 𝐻𝑠𝑏𝑒𝑗𝑏𝑢𝑗𝑝𝑜

▪

The thermal capacitance: 𝐷𝑢ℎ = 𝜍𝑑′𝐵𝑡𝑢𝑏𝑕𝑓ℎ

▪

The thermal time constant: 𝜐𝑢ℎ = 𝐷𝑢ℎ

𝐻𝑢ℎ

t

𝜐𝑢ℎ

Δ𝑈

∆𝑈

𝑡𝑡

𝐻𝑏𝑠𝑛 𝑄𝑝𝑞𝑢

𝒒𝒃𝒔𝒃𝒏𝒇𝒖𝒇𝒔𝒕 𝒃𝒐𝒆 𝒅𝒑𝒐𝒕𝒖𝒃𝒐𝒖𝒕: 𝜍 kg m3 − mass density, c′ J kg ∙ 𝐿 − specific heat capacitance, 𝜃 − 𝑝𝑞𝑢𝑗𝑑𝑏𝑚 𝑓𝑔𝑔𝑗𝑑𝑗𝑓𝑜𝑑𝑧, h − stage height [m]

h

THERMAL MODELING – SOLID CONDUCTION AND RADIATION

8

▪

Body emits radiation according to its temperature: 𝑄𝑠𝑏𝑒 = 𝜁𝜏𝐵𝑢𝑝𝑢𝑏𝑚𝑈

𝑡 4 ≈ 𝜁𝜏 2 ∙ 𝐵𝑡𝑢𝑏𝑕𝑓 𝑈 𝑡 4

▪

Hence, the thermal conductance due to thermal radiation: 𝐻𝑠𝑏𝑒 = 𝑒 Τ 𝑄𝑠𝑏𝑒 𝑒 𝑈 = 8𝜁𝜏𝐵𝑡𝑢𝑏𝑕𝑓𝑈

𝑡 3

▪

The thermal conduction through a material is derived from Fourier law and equals to: 𝐻 = Q ∆𝑈 ∙ ∆𝑢 = 𝑙 ∙ 𝐵 𝑀

▪

For example, in our device, the thermal solid conduction is governed by the holding arm: 𝐻𝑏𝑠𝑛 = 𝑙𝑏𝑠𝑛 ∙ 𝐵𝑏𝑠𝑛 𝑀𝑏𝑠𝑛

𝒒𝒃𝒔𝒃𝒏𝒇𝒖𝒇𝒔𝒕 𝒃𝒐𝒆 𝒅𝒑𝒐𝒕𝒖𝒃𝒐𝒖𝒕: 𝜁 − body emmisivity, 𝜏 = 5.67 ∙ 10−8 𝑋 𝑛2 ∙ 𝐿4 − Stefan– Boltzmann constant, k W m ∙ 𝐿 − thermal conductivity, Astage − stage area m2 , Larm − arm length m 𝑅 − 𝑢ℎ𝑓𝑠𝑛𝑏𝑚 𝑓𝑜𝑓𝑠𝑕𝑧 𝐾 , 𝑈 − 𝑢𝑓𝑛𝑞𝑓𝑠𝑏𝑢𝑣𝑠𝑓 𝐿 , 𝑢 − 𝑢𝑗𝑛𝑓 𝑡 , 𝐵 − 𝑏𝑠𝑓𝑏, 𝑀 − 𝑚𝑓𝑜𝑕𝑢ℎ[𝑛] 𝑩𝑩𝑺𝑵

𝑴𝑩𝑺𝑵 𝑩𝒕𝒖𝒃𝒉𝒇

Arm cross-section TMOS top view schematic

THERMAL MODELING – GAS CONDUCTION AT HIGH PRESSURE

9

▪

The thermal conductivity of gas at high pressure is independent on the pressure and equals to a constant for a given temperature (like solids):

𝒍𝒊𝒋𝒉𝒊−𝒒𝒔𝒇𝒕𝒕𝒗𝒔𝒇 = 𝒅𝒑𝒐𝒕𝒖𝒃𝒐𝒖

𝑿 𝑳∙𝒏

▪ The thermal conductivity of the gas is given by:

𝑙𝑕𝑏𝑡 = 𝟐

𝟒 𝝇𝒅′𝒘𝒏𝒑𝒎 ∙ 𝒎𝒏𝒈𝒒 = 𝐻0 ′′ ∙ 𝑞 𝑞0 ∙ 𝑚𝑛𝑔𝑞 𝑋 𝐿∙𝑛

▪

At high pressure where the collision distance between two gas molecules is much smaller than the device typical

• dimensions. Therefore, the mean-free-path is governed by the molecule collision distance

▪

In this case, at high pressure, the mean-free-path is proportional to the inverse number of molecules - 𝒎𝒏𝒈𝒒 ∝ 𝒐−𝟐, and the pressure is proportional to the number of molecules - 𝒒∝n, where n is the number of molecule

▪ For air at high pressure, the value of 𝒍𝐛𝐣𝐬 is well established and equals to 𝟏. 𝟏𝟑𝟕

𝑿 𝒏∙𝑳 at 300°[K]

𝒅𝒑𝒐𝒕𝒖𝒃𝒐𝒖𝒕 𝒃𝒐𝒆 𝒒𝒃𝒔𝒃𝒏𝒇𝒖𝒇𝒔𝒕: 𝑞 − 𝑞𝑠𝑓𝑡𝑡𝑣𝑠𝑓 𝑄𝑏 , 𝜍 − 𝑛𝑏𝑡𝑡 𝑒𝑓𝑜𝑡𝑗𝑢𝑧 𝑙𝑕 𝑛3 , 𝑑′ − 𝑡𝑞𝑓𝑑𝑗𝑔𝑗𝑑 𝑢ℎ𝑓𝑠𝑛𝑏𝑚 𝑑𝑏𝑞𝑏𝑑𝑗𝑢𝑏𝑜𝑑𝑓 𝐾 𝑙𝑕 ∙ 𝐿 , 𝑤𝑛𝑝𝑚 − 𝑛𝑝𝑚𝑓𝑑𝑣𝑚𝑓 𝑤𝑓𝑚𝑝𝑑𝑗𝑢𝑧 𝑛 𝑡 , 𝑚𝑛𝑔𝑞 𝑛 − 𝑛𝑓𝑏𝑜 𝑔𝑠𝑓𝑓 𝑞𝑏𝑢ℎ, 𝐻0

′′ 𝑋

𝐿 − 𝑜𝑝𝑠𝑛𝑏𝑚𝑗𝑨𝑓𝑒 𝑢ℎ𝑓𝑠𝑛𝑏𝑚 𝑑𝑝𝑜𝑒𝑣𝑑𝑢𝑏𝑜𝑑𝑓 𝑔𝑝𝑠 𝑞0 = 1[𝑄𝑏]

THERMAL MODELING – GAS CONDUCTION AT LOW PRESSURE

10

▪ The thermal conductivity by the gas is given by: 𝒍𝒉𝒃𝒕 = 𝟐

𝟒 𝝇𝒅′𝒘𝒏𝒑𝒎 ∙ 𝒎𝒏𝒈𝒒 = 𝑯𝟏 ′′ ∙ 𝒒 𝒒𝟏 ∙ 𝒎𝒏𝒈𝒒 𝑿 𝑳∙𝒏

▪ At low pressure where the collision distance between two gas molecules is much larger than the

device typical dimensions. Therefore, the mean-free-path is governed by the device smallest typical dimension

▪ In this study, 𝒎𝒏𝒈𝒒 = 𝒉𝒃𝒒 = 𝟒𝝂𝒏 and 𝑯𝟏

′′

𝒒𝟏 ≈ 𝟑

▪

Therefore: 𝒍𝒎𝒑𝒙−𝒒𝒔𝒇𝒕𝒕𝒗𝒔𝒇 = 𝟕 ∙ 𝒒

𝑿 𝒏∙𝑳

Collision Distance between two molecules Collision Distance between molecule to device surface

𝒅𝒑𝒐𝒕𝒖𝒃𝒐𝒖𝒕 𝒃𝒐𝒆 𝒒𝒃𝒔𝒃𝒏𝒇𝒖𝒇𝒔𝒕: 𝑞 − 𝑞𝑠𝑓𝑡𝑡𝑣𝑠𝑓 𝑄𝑏 , 𝜍 − 𝑛𝑏𝑡𝑡 𝑒𝑓𝑜𝑡𝑗𝑢𝑧 𝑙𝑕 𝑛3 , 𝑑′ − 𝑡𝑞𝑓𝑑𝑗𝑔𝑗𝑑 𝑢ℎ𝑓𝑠𝑛𝑏𝑚 𝑑𝑏𝑞𝑏𝑑𝑗𝑢𝑏𝑜𝑑𝑓 𝐾 𝑙𝑕 ∙ 𝐿 , 𝑤𝑛𝑝𝑚 − 𝑛𝑝𝑚𝑓𝑑𝑣𝑚𝑓 𝑤𝑓𝑚𝑝𝑑𝑗𝑢𝑧 𝑛 𝑡 , 𝑚𝑛𝑔𝑞 𝑛 − 𝑛𝑓𝑏𝑜 𝑔𝑠𝑓𝑓 𝑞𝑏𝑢ℎ, 𝐻0

′′ 𝑋

𝐿 − 𝑜𝑝𝑠𝑛𝑏𝑚𝑗𝑨𝑓𝑒 𝑢ℎ𝑓𝑠𝑛𝑏𝑚 𝑑𝑝𝑜𝑒𝑣𝑑𝑢𝑏𝑜𝑑𝑓 𝑔𝑝𝑠 𝑞0 = 1[𝑄𝑏] = 𝑚𝑛𝑔𝑞= 𝑕𝑏𝑞

THERMAL MODELING – GAS CONDUCTION AT INTERMIDATE PRESSURE

11

▪ At intermediate pressure, the thermal conductivity is given by the parallel combined of the both mechanisms:

1 𝑙𝑕𝑏𝑡 = 1 𝑙ℎ𝑗𝑕ℎ−𝑞𝑠𝑓𝑡𝑡𝑣𝑠𝑓 + 1 𝑙𝑚𝑝𝑥−𝑞𝑠𝑓𝑡𝑡𝑣𝑠𝑓

THERMAL MODELING - SUMMARY

12

▪

The holding arm conduction does not depend on pressure

▪

Typical CMOS-SOI thermal properties required for thermal simulation:

▪

Air conduction is governed by two mechanisms: at low pressure and high pressure

▪

This study evaluates this pressure impact on the thermal conductance of the packaged device

▪

The air thermal properties calculated by the ideal gas law and by the method showed in the previous slides

THERMAL MODELING – BOUNDARY CONDITIONS

13

▪

3D model of the device was generated in FEA software

▪

Materials thermal properties were assigned

▪

Applying boundary conditions to our packaged model:

▪

Simulations for wide pressure range values were performed

Constant temperature of 𝟑𝟏𝟏[𝑫] on the outer package 1𝝂𝑿 𝒑𝒐 𝒇𝒃𝒅𝒊 𝒕𝒗𝒕𝒒𝒇𝒐𝒆𝒇𝒆 𝒕𝒖𝒃𝒉𝒇

MEASUREMENT AND SIMULATIONS RESULTS OF 𝝊𝒖𝒊 AND 𝑯𝒖𝒊

14

Steady-state thermal simulations yield the increase of the sensors temperature:

∆𝑼

The thermal conductance obtained from the heat balance equation:

𝑯𝒖𝒊 = 𝑸 ∆𝑼

The thermal time constant can be

• btained by transient simulation or

can be evaluated by:

𝝊𝒖𝒊 = 𝑫𝒖𝒊 𝑯𝒖𝒊

▪ There is no simple way to measure the temperature of the physical device ▪ Best way to measure or evaluate the thermal performance of the device is by measure the thermal time constant

𝑞 = 2.5 𝑄𝑏 𝑢𝑓𝑛𝑞𝑓𝑢𝑏𝑢𝑣𝑠𝑓 𝑠𝑏𝑜𝑕𝑓: 20° − 28°[𝐷] 𝑞 = 105 𝑄𝑏 𝑢𝑓𝑛𝑞𝑓𝑢𝑏𝑢𝑣𝑠𝑓 𝑠𝑏𝑜𝑕𝑓: 20° − 20.215°[𝐷]

20.095°[𝑫] 20.215°[𝑫] 20.191°[𝑫] 20.167°[𝑫] 20.143°[𝑫] 20.119°[𝑫] 20.072°[𝑫] 20.0𝟓𝟕°[𝑫] 20.024°[𝑫] 20°[𝑫] 23.557°[𝑫] 28.084°[𝑫] 27.115°[𝑫] 26.226°[𝑫] 25.336°[𝑫] 24.447°[𝑫] 22.668°[𝑫] 21.779°[𝑫] 20.889°[𝑫] 20°[𝑫]

[Pa]

[Pa]

CONCLUSIONS

15

▪ With this modeling the optimal pressure may be selected ▪ Highest performance devices require residual pressure of few pascals ▪ The modeled, simulated and measured thermal time constant are in good agreement

ACKNOWLEDGMENTS

16

▪

The generous funding of TODOS TECHNOLOGIES Ltd. (https://www.todos-technologies.com) is gratefully acknowledged. TODOS TECHNOLOGIES holds exclusively the IP related to this work

▪

The devices were fabricated and packaged at ST Microelctronics. The excellent work of all the engineers supporting this work is highly appreciated